unity: set env variables for global menu

Fixes #869.
unity: fix Unity HUD (alt key menu)

Fixes #802.
unity: move hacks into profiled and autostart
unity: quote window-stack-bridge
unity: code review fixes
unity: unify common service launching code
unity: remove useless local in execfromconf
Merge pull request #900 from smibarber/fix-global-menu

Fix Unity global menu and HUD
store chroots in /home/chronos for free encryption