Support unknown chunks in the GUI

+ Add UnknownChunkController
+ Implement UnknownChunk.Type
Use MysteryBox for unknown chunks
Remove the CreateEditor override for UnknownEntryController
Remove some unnecessary using directives
Add support for T2 chunks

+ Add T2Chunk
+ Add T2ChunkLoader
+ Add T2ChunkController
Add Crash 1 beta to README supported list
Change PAL BETA to EU BETA in README