Multiclick support for builders

This commit adds multiclick support for builders and also a little
example about how to use multi click.
Merge pull request #250 from relu91/1.4

Multiclick support for builders
Merge pull request #255 from 3xp0n3nt/libgdx-cleanup

Minor LibGDX examples cleanup.
Update <nifty.version> to 1.4.1-SNAPSHOT to fix compiler errors
Add music looping to GdxMusicHandle.
Fix NiftyStandardInputEvent.Activate bug.

NiftyStandardInputEvent.Activate only simulates a mouse click, but not a
mouse release. This causes bugs where only listening for
ButtonReleasedEvent's but not ButtonClickedEvent's for a specific button
will cause input mappings to NiftyStandardInputEvent.Activate to not
work with that button. This results in undesirable & unexpected behavior
such as pressing the enter key on a currently focused button does not do
anything.

The solution is to make NiftyStandardInputEvent.Activate simulate a
mouse click and a mouse release.