Mouse grabbing, minor improvements

* Mouse grabbing was implemented, meaning you can hide (and un-hide) the
cursor, for example in keyboard-only games.
* The Camera's freeMode method can be given destination and speed
parameters, which will make it move there instead of staying where it
is. Also, you can provide a value of -1 for speed to make it move in an
instant.
* The ShapeRenderer takes doubles as color parameters, so you do not
have to do the casting manually.
* Since many operating systems tend to repeat key events when a key is
held down, whether this happened can be gathered from the Keyboard
class' KeyTypeEvent.
* TiledLevel allows you to convert screen coordinates into tile
coordinates, optionally taking the camera offset into account.
* ScreenLoading now displays the text in the correct size even on low
resolutions.
* Javadoc fixes and updates.