Added frame stepping button.

Signed-off-by: Jared Woolston <jwoolston@tenkiv.com>
Merge commit '9b97c7c0c6e60006b3238aa67d05e38957df3b5f' into scenegraph
Fix for crash on removing object.

Signed-off-by: Jared Woolston <jwoolston@tenkiv.com>