Merge pull request #477 from Choran66/master

Modal , Validations and Gestures
ObservableCollection<T> casting bug fix
Merge branch 'master' into repeater-bug-fix
RepeaterView<T> index bug fix
event handler bug fix
Added HttpHandler with cookie callback
Geo prompt fix for Android

https://github.com/sami1971/Xamarin-Forms-Labs/commit/68ab626d944ff84dc6
e5ac677c6f1ab40d27c46e#commitcomment-8540619
Fix for iPhone6+ screen resolution
Added status code to WebResponseException
Added support for Post/Put requests without request content (not required by the spec)
Merge pull request #483 from TheXenocide/master

Simple IRestClient additions
Merge pull request #479 from gyuwon/repeater-bug-fix

Repeater bug fix
Merge remote-tracking branch 'upstream/master'
Extracted the collectionChangedHandle to it's own first class...err class

Extracted collectionChangedHandle to it's own file, and extended it to
handle ItemCollectionChanged events internally, thus further simplifying
control code.
Added lifecycle events to the Carousel view via an interface that
viewmodels can optionally implement.