Added placeholder text color property to ExtendedEntry and implemented it on iOS
Added ExtendedEntryRenderer for Android supporting  PlaceholderTextColor property
Merge commit '8a068161d39be70445b87198918045854ad397cc'

Conflicts:
	src/Xamarin.Forms.Labs/Xamarin.Forms.Labs.Droid/Xamarin.Forms.Labs.Droid.csproj
Added ExtendedEntry in Xamarin.Forms.Labs.Droid project.
Merge pull request #290 from Applifting/master

ExtendedEntry - Added text placeholder color (iOS, Android)