Changes:
- `ShowDevelopmentWarning` is now under the '[Interface]' group in
Dolphin.ini, with other interface-related settings. So, whoever uses
DolphinQt will have to edit that manually again. Sorry!
- Game search paths and the last file are now shared properly with
DolphinWX
- Qt-only preferences like "Preferred View: list/table" are now
stored using the platform's native settings storage, rather than in
UI.ini
At first there weren't many enums in Volume.h, but the number has been
growing, and I'm planning to add one more for regions. To not make
Volume.h too large, and to avoid needing to include Volume.h in code
that doesn't use volume objects, I'm moving the enums to a new file.
I'm also turning them into enum classes while I'm at it.
