Ran cpp11-migrate on game/*.cc.

- Most of the work done automatically by the tool
- Headers are not touched by the tool
- Manual review of all changes, additional cleanup by hand
- Miscellaneous other changes such as const-correctness fixes
- Mic pass-through no longer assumes (hard-coded) 48 kHz output
- Removed song preloading hack (breaks cover flashing in song browser)
- It still compiles, let's ship it!