Added gradle support for running texturePacker at build time.

Make sure the proper ext.texturePacker parameter is set in the toplevel
gradle.build file and have TexturePacker run with those whenever the
"texturePacker" task gets invoked, e.g. "./gradlew texturePacker
desktop:run".
Merge branch 'master' of github.com:mariusk/libgdx

Conflicts:
	extensions/gdx-setup/src/com/badlogic/gdx/setup/resources/build.gradle
Merge pull request #1274 from mariusk/master

Added gradle support for running texturePacker at build time.