Merge mp3 support from Orphis' old FFMPEG code.

Conflicts:
	CMakeLists.txt
	Core/HLE/sceAudio.cpp
	Core/HLE/sceMp3.cpp
	Core/HLE/sceMpeg.cpp
Uncomment some unused stack-corrupting code from sceMp3Decode. Update ffmpeg.
Fix sceMp3 build without USE_FFMPEG
Fix crash in mp3 reading.
Merge pull request #1786 from unknownbrackets/mp3-support

Fix crash in mp3 reading
Get mp3 sample rate and channels from FFMPEG instead of trying to detect ourselves.
VERBOSE a log statement
Fix possible savestate/shutdown issue.
Toggle to adjust opacity in UI Controls
Switch handlers from std::vector to std::map, add a max handler count, and return an error if too many handlers exist.
Adjust by +5/-5 , relaod cheat show only when enabled cheat
Merge pull request #2332 from thedax/sceUtilityFix

Fix possible savestate/shutdown issue.
Merge pull request #2336 from thedax/sceNetStubsCrashFix

Rewrite some of the sceNetAdhocctlAddHandler/DelHandler code
Merge pull request #2338 from oioitff/atrac-fix

Bug fix for sceAtrac.
Keep EmuThread running on game shutdown.

Especially relevant for games that call sceKernelExitGame(), like most
homebrew.  Otherwise, EmuThread actually quits and we can't continue.
Merge pull request #2340 from unknownbrackets/windows-ui

Keep EmuThread running on game shutdown
Merge pull request #2333 from raven02/patch-1

Toggle to adjust opacity in UI Controls
Toggle to adjust on-screen buttons scaling
Merge pull request #2341 from raven02/patch-2

Toggle to adjust on-screen buttons scaling
Add multple save/load slot in UI Pause Menu