add PIUIO_Leds driver

The mappings in this driver are specific to the piuio kernel driver, but
once lights mapping is possible this could be made into a generic leds
class driver.
remove the ssc part from the Name in stepmania.desktop
don't set lights for nonexistent lights

duh.
point at the right file in the filesystem
Added WheelItemBase:IsLoaded lua function and associated error.
Change LifeDifficulty to match StepMania 3.9's again (4=1.0)
Changed Actor:scale_or_crop_background back to forcing the actor to the screen center.  Changed LogDisplay's IgnoreIdentical to not ignore when hidden.
Added Swap Up/Down option to Edit Alter Menu.
Added Arbitrary Remap option to Alter Menu in Edit Mode.
fix StageDisplay errors, EvalSummary
Implement ScreenContinue
Fix eval branch. Course mode fix
Changed ColorDepth prefs defaults to 32-bit.
Update metrics.ini
Merge pull request #284 from Midiman/changes-beta4

Beta 4 theme updates
Added FastNoteRendering preference.
Merge pull request #276 from djpohly/piuio-leds

LightsDriver for /sys/class/leds with new PIUIO kernel module
Implement ScreenCaution, fix CDTitle
Merge branch 'changes-beta4' of https://github.com/Midiman/stepmania
Merge branch 'master' of https://github.com/stepmania/stepmania