Implement ActionBar component

[rigor789]

Implement ActionBar component

[EddyVerbruggen]

This will be the API. Working nicely now on iOS and Android, but will need to test a few more things before creating a PR:

<action-bar :title="subreddit">
  <navigation-button text="Back!" android.systemIcon="ic_menu_back" @tap="navigationButtonPressed"></navigation-button>
  <action-item android.systemIcon="ic_menu_refresh" ios.systemIcon="13" @tap="refresh"></action-item>
  <action-item text="change" android.position="popup" ios.position="right" @tap="chooseSubreddit"></action-item>
</action-bar>

[tjvantoll]

Minor note: might want to rename from AppBar to ActionBar, as that’s the name NativeScript uses.

[EddyVerbruggen]

Working on this one atm!

[rigor789]

Very nice @EddyVerbruggen! Can't wait to test that :)

[EddyVerbruggen]

Would be cool if you could take a look, @rigor789!

I've adjusted the listview and tab samples to include an action-bar, making them look like this:

[rigor789]

This has been added in #34

If any issues arise, open a new issue. Closing this one