Adds interfaces IReadOnlyCollection and IReadOnlyDictionary.
Merge remote-tracking branch 'prodigysim/readonlydict2' into roslyn

Conflicts:
	Runtime/CoreLib.Script/Dictionary.js
	Runtime/CoreLib.Script/ICollection.js
	Runtime/CoreLib.Script/IDictionary.js
	Runtime/CoreLib.TestScript/CoreLib.TestScript.csproj
	Runtime/CoreLib.Tests/Core/CoreLibTests.cs
Fixes for read-only collection interfaces