Make IReactiveCollection an actual Collection
ReactiveCollection => ReactiveList
Fix up Xamarin.Mac
Add read only interfaces for reactive collections

fixes #267
Merge pull request #290 from reactiveui/readonly-collections

Add read only interfaces for reactive collections
Merge branch 'the-great-collection-rename' into rxui5-master

Conflicts:
	ReactiveUI.Tests/ReactiveCommandTest.cs
Merge branch 'rxui5-master' of https://github.com/reactiveui/ReactiveUI into rxui5-master