Merge pull request #987 from SeiferTim/dev

My `FlxPreloader` changes
Add button IDs for Dualshock 4
FlxKeyboard: improve the firstPressed-function implementations

- now returning the string name instead of a FlxKey
- now returning "" instead of null when no key was found
Trying to fix `FlxPreloader`... again...
Changed `minDisplayTime` back to something small...
Merge pull request #989 from massivedanger/ps4-controller-support

Add button IDs for Dualshock 4
Remove unnecessary @default from docs
FlxSprite / FlxTilemap: fix the order of drawDebug(), fixes #988

needs to happen *after* the actual draw() logic
FlxSignalTest: add null tests back
FlxSignal code style
Fix tests

no return values for add() (yet)
Make it easier to play FlxSplash in debug mode
Merge branch 'dev' of https://github.com/HaxeFlixel/flixel into dev