* mysql: pass timerange for template variable queries
* mysql: document time range macro usage in template variables
* mysql: docs for on time range change refresh mode for template queries
* Revert "mysql: docs for on time range change refresh mode for template queries"
This reverts commit 5325972aa4f66257aa20f7ae6d4de8fa8fe628b6.
If the template variable query has two columns named __text and __value
then return a list of key values. The value is used when the variable is
interpolated in the query. Allows mapping of texts to ids.