enhances the action menu

This PR was #7256  but i messed up that branch learning about rebasing.

- combines the back/cancel options 
- centers the menu
- unavailable choices dont show
- unbound quicksave/debug/suicide dont show.

- new signature for uimenu to allow 'cancelable'
- fixes uimenu to render '!' 

https://imgur.com/a/mN8Yh screenshots with the key changes.