res:dock:: fix tray icon position problem.

when tray icons are changed, the position is not changed.

reason:
change the way to handle Changed event before, to try to fix region problem,
the position is not handled.
app:dock:: add more info to output
res:dock:: make a check for preview window.

the xid of preview window may not be existed.
schema:dock:: add display-mode to dock
common/js/accounts.coffee::delete unused sessionn dbus
common/js/power.coffee::remove session dbus of power_force_session
common/js/power.coffee::remove session dbus of power_force_session; move greeter DBus.session from config to lock.coffee of enableZoneDetect
lock::fixed mediacontrol:: 1.if the player is launched , but stopped, there lock hasnt mediacontrol.  2. if the player is stopped, and the voice img is mute before user mouse over it and wheel
res:dock:: fix tray icon expands problem.

the items is not clean on the right place.