[2/2] Forward port power connect/disconnect notification support

Original commit info:

    [2/2] Power connect/disconnect notification support

    part 1/2: frameworks/base PowerUI and Settings
    http://review.cyanogenmod.org/#/c/35241/

    part 2/2: packages/apps/Settings Sound settings
    http://review.cyanogenmod.org/#/c/35242/

    Change-Id: I7ddd8a47ae4f9a62c586023d151ac42bbe8424c7

    Power sound notifications: fix ringtone picker title

    Change-Id: Ied0a08ec1607b778324e69a7b40bac056235bebf

    Settings: Rename 'Power sounds' to 'Charging sounds' and add summary

    Change-Id: I1cb872917e2d03f0a1c77c25c27f2a0496f9bc05

Change-Id: Ibde52fcd6fd0fabc9eeefc7e6f5a3971527285d7