Further tidy-ups
- Consolidate .gitignore files now that we're using CApp so no directories need to be pre-created
- Remove obsolete Debug subdirectory
- Tweak install_themedefs rule to use InstRes, permitting cross-compilation
- Rename the DiscSprites files to suit InstRes
- Resources.Draw.Sprites was being included twice in the ROM - once in the Messages module and once embedded within the Draw module - now only include within Messages (via resources rule)