vendor: support custom unofficial build tags

By defining TARGET_UNOFFICIAL_BUILD_ID in a device's cm.mk, users can
build custom CM builds with their own identifier in place.
This adheres to CM's policy that unofficial builds must be
marked as such, as both the filename and internal version will still
contain the word UNOFFICIAL.

Example:
TARGET_UNOFFICIAL_BUILD_ID := CatEater01
results in
cm-11-20131211-UNOFFICIAL-CatEater01-device(.zip)

Change-Id: I61acdf4698a7fe2b35d3d5315be4b444b1b97987
overlay: Fix Keyguard configuration

In 4.4 Keyguard has moved to a separate package
Move its config options to the proper overlay

Change-Id: I0a57874f3ef7702c6407485e98e1d10169baa0ac
Merge "overlay: Fix Keyguard configuration" into cm-11.0
Merge "vendor: support custom unofficial build tags" into cm-11.0
Merge remote-tracking branch 'cm/cm-11.0' into wszf