Added missing ctor.

closes #209
Fixed opacity with cascadeOpacityEnabled.

closes #237
Moved scheduleUpdate to onEnter, added unscheduleUpdate onExit.

closes #230
Added null checks for add/set animation.

closes #173
Fixed null check.
Organized spine-libgdx so tests and the skeleton viewer are separate.
Added bone width to debug renderer.
Fixed NPE if file failed to load.
Merge branch 'master' of https://github.com/EsotericSoftware/spine-runtimes