update OSX mkrelease scripts

This allows OS X devs to bundle either a release or a nightly disk image.  See the updated readme for more information.
Merge pull request #286 from dguzek/OSX-bundle-script

update OSX mkrelease scripts
Fix up HowToPlay graphics
Fix up HowToPlay graphics (2)
Make TwoPartSelection dialog work for all players
Make TwoPartSelection dialog hide on events
ScoreDisplay has actual shadows now...
Merge branch 'changes-beta4' of https://github.com/Midiman/stepmania
Continue now goes to SelectStyle. Fixes error
TwoPartSelection noteskin for pump only, routine skins
Merge branch 'changes-beta4' of https://github.com/Midiman/stepmania
Add people to credits.
Remove non-working Export Packages for now; might add later if it works again
Update ScreenHowToPlay elements to use localized strings