Added DI interfaces for Resolver & Container

Simple Resolver interface acts as a generic resolver that can be
implemented using 3rd party DI containers. Hopefully this can somehow
be used to extend Xamarin DependencyResolver.

I will put in some 3rd party wrappers into Plugins project later on. I
have tested about 5 of them and some are PCL compatible while others
only work with WP8 and/or Android. There is a simple container
implementation as well to give a little more features than
Xamarin.Forms container.
Merge branch 'master' of https://github.com/XForms/XForms-Toolkit

Conflicts:
	samples/XForms.Toolkit.Sample/App.cs
Added Battery service to device

Battery service added.
Device page added to the tabs with extended device information on the
second carousel page: display info + battery info
Fixes to battery service frame
Added interfaces for caching

ISimpleCache cache interface without expiration,
ICacheProvider:ISimpleCache with expiration support.
Add simple ViewModel based NavigationService
Added serializer interfaces and extensions

Serialization interfaces for stream, string and byte serializers.
Plugins for Json.NET, ServiceStack, ProtoBuffer to follow. These are
needed for SQLite.Net caching so we can store serialized objects to
data tables and easily support BLOB fields for complex objects.
Added SQLite.Net.Async cache provider
Updated Forms nuget and renderers for IOS and Android
Merge branch 'viewmodel-navigation'
Updating samples
Include mvvm sample
Updated WP sample
Added serializer plugins

In the main package XML and JSON serializers using the runtime
serializers. As plugins the 3rd parties:

Json.NET (portable)
ServiceStack V3 (NET45, iOS, Android & WP8 versions) - only JSON
serializers for now
ProtoBuf.Net (portable)
Merge branch 'master' of https://github.com/XForms/XForms-Toolkit

Conflicts:
	src/XForms.Toolkit/XForms.Toolkit.WP/XForms.Toolkit.WP.csproj
Fix mvvm navigation sample
Update README.md
Update README.md
Update README.md
Screenshots for iOS and Android