Add support for TRR

[lahm86]

• [ ] Make TRGE pretend there is a gameflow and proceed normally with backups. Carry over logic for writing level files back
• [ ] Update UI and core to recognise TRR
• [ ] Work out what can and cannot be supported...

Audio TR1 now uses MAIN.SFX but it's not yet clear where sample indices are defined - those in .PHD seem to be completely ignored.

Items Item limit remains 256 in TR1 and TR3. TR2 seems to be 257.

Textures TexInfo limit is 4096. TPage limit is 32.