Add dark themes for dialogs and alert dialogs:

A dark material theme with a blue grey background,
and a color accent from the light version of the material theme.

- Apply the new theme to the Power-, reboot menu and the shutdown dialog

Conflicts:
	core/res/res/drawable/ic_lock_reboot_dark.xml
	core/res/res/values/dk_symbols.xml
	policy/src/com/android/internal/policy/impl/GlobalActions.java
	services/core/java/com/android/server/power/ShutdownThread.java