Allow custom order of groups via Extension method

Allows the ability to control the way groups are ordered in the
ItemsShowcaseView
Merge pull request #37 from acrow59/master

Icon Maker & App Builder Update
Fix Snap Layout in ItemDescriptionView
Merge branch 'master' of https://github.com/winappkits/XPlatformCloudKit
Change opacity of Wallpaper when View is snapped
Stop SearchPane launching when using keyboard

Users may want to interact with html description (for example including
an html based calculator) but keyboard would always divert input to the
SearchPane.  Also, QuerySubmitted was being subscribed to multiple
times, moved to one-time execution block.
Hide ad control when in snapped view
Hide webView and button when in Filled State
Fix bug in detecting expired cache
Add more aesthetic flipView transition on swipe
Auto Size the WebViewFullScreenToggleButton
Update README.md
Add Experimental OAuth / Twitter Support
Rollback package upgrades introduce by AsyncOAuth

For unknown reasons this was breaking the WP8 build, fixed by rolling
back.  Twitter confirmed working on WP8 with OAuth with this changeset.
Twitter Support added to Droid Project
Update README.md
Remove Win8 / WinPhone only warning for Twitter 

Droid Project now supports TwitterService
Add Support for Youtbe Data API v3

Youtube has announced dropping support for the V2 API:
https://developers.google.com/youtube/2.0/developers_guide_protocol_deprecated

Keeping with the recent Twitter Support update to XPCK, it has spawned a
new method of support for 3rd party APIs marked by the  creation of a
3rd Party Services region in AppSettings.cs.  Many API providers are
moving away from RSS in favor of custom, often Oauth2.0 required and
JSON-only output formats.  Given that there is no standard format for
parsing JSON output from 3rd Party APIs it makes sense to create a
customized  parser and DataService in order to accommodate these
services.

To create your own service, in the PCL project, add a new section to
AppSettings.cs under 3rd Party Services then create a new service under
DataServices that implements IDataService.  Your service must properly
return a List of type Item as enforced by IDataService.  Finally, add a
condition to DataServices\DataServiceFactory to ensure your DataService
is loaded based on some custom condition.  Doing this will afford you
cache support and default ordering of the data returned by your new
service.

*Refactor RssSource and TwitterSource to generic UrlSource (This will
make creation of new DataServices more straightforward)
*Add YoutubeService REQUIRES API KEY FROM GOOGLE

Issues: YoutubeService can get all videos for a given playlist id but
appears to break at 130 results.  This is likely an issue with Google's
incomplete API but is planned to be investigated further to determine
absolute cause.
Disable YoutubeService by default
Add support for remote hosted YoutubeSources