Postgres Data Source (#9475)

* add postgresql datasource

* add rest of files for postgres datasource

* fix timeseries query, remove unused code

* consistent naming, refactoring

* s/mysql/postgres/

* s/mysql/postgres/

* couple more tests

* tests for more datatypes

* fix macros for postgres

* add __timeSec macro

* add frontend for postgres datasource

* adjust documentation

* fix formatting

* add proper plugin description

* merge editor changes from mysql

* port changes from mysql datasource

* set proper defaultQuery for postgres

* add time_sec to timeseries query
accept int for value for timeseries query

* revert allowing time_sec and handle int or float values as unix
timestamp for "time" column

* fix tslint error

* handle decimal values in timeseries query

* allow setting sslmode for postgres datasource

* use type switch for handling data types

* fix value for timeseries query

* refactor timeseries queries to make them more flexible

* remove debug statement from inner loop in type conversion

* use plain for loop in getTypedRowData

* fix timeseries queries

* adjust postgres datasource to tsdb refactoring

* adjust postgres datasource to frontend changes

* update lib/pq to latest version

* move type conversion to getTypedRowData

* handle address types cidr, inet and macaddr

* adjust response parser and docs for annotations

* convert unknown types to string

* add documentation for postgres datasource

* add another example query with metric column

* set more helpful default query

* update help text in query editor

* handle NULL in value column of timeseries query

* add __timeGroup macro

* add test for __timeGroup macro

* document __timeGroup and set proper default query for annotations

* fix typos in docs

* add postgres to list of datasources

* add postgres to builtInPlugins

* mysql: refactoring as prep for merging postgres

Refactors out the initialization of the xorm engine and the query logic
for an sql data source.

* mysql: rename refactoring + test update

* postgres:refactor to use SqlEngine(same as mysql)

Refactored to use a common base class with the MySql data source.

Other changes from the original PR:
- Changed time column to be time_sec to allow other time units in the
future and to be the same as MySQL
- Changed integration test to test the main Query method rather than
the private transformToTable method
- Changed the __timeSec macro name to __timeEpoch
- Renamed PostgresExecutor to PostgresQueryEndpoint

Fixes #9209 (the original PR)

* postgres: encrypt password on config page

With some other cosmetic changes to the config page:
- placeholder texts
- reset button for the password after it has been encrypted.
- default value for the sslmode field.

* postgres: change back col name to time from time_sec

* postgres mysql: remove annotation title

Title has been removed from annotations

* postgres: fix images for docs page

* postgres mysql: fix specs

public/app/plugins/datasource/postgres/partials/annotations.editor.html

@@ -0,0 +1,41 @@
+
+<div class="gf-form-group">
+  <div class="gf-form-inline">
+		<div class="gf-form gf-form--grow">
+			<textarea rows="10" class="gf-form-input" ng-model="ctrl.annotation.rawQuery" spellcheck="false" placeholder="query expression" data-min-length=0 data-items=100 ng-model-onblur ng-change="ctrl.panelCtrl.refresh()"></textarea>
+		</div>
+	</div>
+
+  <div class="gf-form-inline">
+    <div class="gf-form">
+      <label class="gf-form-label query-keyword" ng-click="ctrl.showHelp = !ctrl.showHelp">
+        Show Help
+        <i class="fa fa-caret-down" ng-show="ctrl.showHelp"></i>
+        <i class="fa fa-caret-right" ng-hide="ctrl.showHelp"></i>
+      </label>
+		</div>
+  </div>
+
+  <div class="gf-form"  ng-show="ctrl.showHelp">
+		<pre class="gf-form-pre alert alert-info"><h6>Annotation Query Format</h6>
+An annotation is an event that is overlayed on top of graphs. The query can have up to four columns per row, the time column is mandatory. Annotation rendering is expensive so it is important to limit the number of rows returned.
+
+- column with alias: <b>time</b> for the annotation event. Format is UTC in seconds, use extract(epoch from column) as "time"
+- column with alias <b>title</b> for the annotation title
+- column with alias: <b>text</b> for the annotation text
+- column with alias: <b>tags</b> for annotation tags. This is a comma separated string of tags e.g. 'tag1,tag2'
+
+
+Macros:
+- $__time(column) -&gt; column as "time"
+- $__timeFilter(column) -&gt;  column &ge; to_timestamp(1492750877) AND column &le; to_timestamp(1492750877)
+- $__unixEpochFilter(column) -&gt;  column &gt; 1492750877 AND column &lt; 1492750877
+
+Or build your own conditionals using these macros which just return the values:
+- $__timeFrom() -&gt;  to_timestamp(1492750877)
+- $__timeTo() -&gt;  to_timestamp(1492750877)
+- $__unixEpochFrom() -&gt;  1492750877
+- $__unixEpochTo() -&gt;  1492750877
+		</pre>
+	</div>
+</div>