Added AnimSpec class for animation pointers
Added AbstractPropertyEvent, updated ShipPE
Minor tweaks to events
Added MutableBool to NamedProperties
Added door open/close on click, other changes...

- Changed LoadingScreen & TestScreen viewports to ScreenViewport
(prevents stretching)
- Added some more layers/notes to TestScreen's main stage
- Changed shipActor's position (bugged when window is shown, need to
resize to update it)
- Added several constants to OVDConstants, pertaining to doors