Binjson7

- Fixed issue with PSGetIndex
- Added IConvertableImmutable and IDeepClonable to support fast cloning and correct immutable to mutable conversion behaviors.
- Add weak caching to BinJSON to ensure same elements returned if sub-object referenced twice (supports correct mutability conversion behavior).
- Implemented IDeepClonable on Array, Expando, and BinJsonObject.
- Implemented IConvertibleImmutable on Array and BinJsonObject and BinJsonArray.
- Added basic conversion tests for BinJSON to test suite.
- Removed non-working pscorlib and PlayScript.Dynamic from build.