Bug 1101170 - Move sandbox status info into a separate module.

Also removes the no-op wrappers for Set*Sandbox when disabled at build
time; nothing used them, one of them was unusable due to having the wrong
type, and all they really accomplish is allowing sloppiness with ifdefs
(which could hide actual mistakes).
Bug 1101170 - Move Linux sandbox code into plugin-container on desktop.
Bug 1101170 - Move GMP's LinuxSandboxStarter into plugin-container.