Fixes#915
BREAKING CHANGE: Before, if you did not have a `title` attribute set on your
ion-view, it would transition into that view and erase the navbar's current
title.
Now, if your ion-view does not have a `title` attribute set, the new
view will be transitioned in, but there will be no title change.
If you wish to have a blank title on your new view, you must now
explicitly set your `ion-view`'s title attribute to an empty string.
To migrate your code, change from this:
```html
<ion-view></ion-view>
```
To this:
```html
<ion-view title=""></ion-view>
```
BREAKING CHANGE: All directives are now prefixed with `ion-`.
For any directive you use, add the ionic prefix.
For example, change this HTML:
```html
<tabs>
<tab title="home" href="/tab/home">
<content>Hello!</content>
</tab>
</tabs>
```
To this HTML:
```
<ion-tabs>
<ion-tab title="home" href="/tab/home">
<ion-content>Hello!</ion-content>
</ion-tab>
</ion-tabs>
```
Starting a couple of versions ago, animations in navbar stopped working.
I took this as a chance to fix this, and ddo a refactor to make the code
more modular and testable.
Lots of manual dom manipulation was offloaded to angular directives, and
now we will not have bugs with end-user using interpolated class
attribute on their own nav-bar and overriding our own manually added
classes.
