Multiclick support for builders

This commit adds multiclick support for builders and also a little
example about how to use multi click.
Minor LibGDX examples cleanup.

- Upgrade Nifty version in LibGDX examples. Pom value in nifty-examples-libgdx
  pom incorrectly specifies 1.4.0. Change to 1.4.1-SNAPSHOT.

- Fix LibGDX android examples. Remove nonexistent configuration value
  'useGL20'.
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.