Toggle nav bar through power menu (1/2)

- This is highly based on this commit form SlimRoms: https://github.com/SlimRoms/frameworks_base/commit/4097a175f00fa0137169c4ae4a6bc35a2799c97f
- Now we can toggle nav bar on/of in power menu. It's easier to use PIE.

Thanks again to @kufikugel

Codes ported and new codes from @cristianomatos

Change-Id: I75ea9623d3701fc01ec56a504be5e6a5fcad3cc1

Conflicts:
	core/res/res/values/pac_symbols.xml
	policy/src/com/android/internal/policy/impl/GlobalActions.java