Bug fixes and API changes

[kairusds]

Small patch.

Added

• Config.getSkins() and Config.addSkin API

Removed

• Avg offset statistics display
• OSZParser
• SkinImporter

Changes

• Update free memory text on debugging to be more readable
• Replace OSZParser and SkinImporter with FileUtils.extractZip()
• Move OSZParser.canUseSD() to FileUtils
• Update SkinPathPreference.reloadSkinList() to use the Config.getSkins() API and fix the Graphics settings menu crash
• Update MainScene to load beatmaps imported from the Downloads folder and add skin import functionality when the Play button is pressed
• Update CursorSprite to use a global variable for checking OsuSkin.get().isRotateCursor() and remove isShowing value on update()
• Update CursorEntity to comment out handleLongerTrail, add setVisible() on setShowing() and add an isShowing check on update()