GC games with long names store two variations of the name in
opening.bnr. This makes the shorter of those names available.
For volumes other than GC discs, prefer_long is ignored.

ISOFile and GameFile were using IsWiiDisc() and IsWadFile() to set
an enum value. The volume might as well return an enum directly.

I increased the Qt CACHE_REVISION because m_platform now is saved as u32
instead of int, but increasing the wx CACHE_REVISION is not necessary.

Disc number is changed from bool to u8, and revision is changed from
int to u16 (WADs can use all 16 bits, but discs can only use 8 bits).

This makes Dolphin display the same names as the Disc Channel.

This makes the code cleaner and also leads to some user-visible changes:

The wx game properties will no longer let the user
select WAD languages that don't have any names.

The Qt game list will now display names using the languages
set in the configuration instead of always using
English for PAL GC games and Japanese for WADs.

If a WAD doesn't have a name in the user's preferred language,
English is now selected as a fallback before Japanese.