status bar power menu: use constants

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBarHeaderView.java
status bar power menu: be sure to update visibility when showing qs details

fix status bar power menu icon showing up if previously disabled
step to reproduce:
- enable status bar power menu
- disable it
- pull down qs and tap data icon
- close data details
- status bar power menu icon will be visible even if disabled

thanks @enricocid for the bug report
Prevent wrong system ui visibility callback after the user swipe

If we return vis without clearing clearable flags, it will be set to
IStatusBarService in updateSystemUiVisibilityLw(), and then be
callbacked to WMS via statusBarVisibilityChanged(), and then be
dispatched to the client; which is wrong because WMS should dispatch
the new value to the client, not the old one.

https://code.google.com/p/android/issues/detail?id=79991

Change-Id: I2a06d1fbe66e854e639d86a39784f8c6a3303674