framework: Custom lock screen background [1/2]

Patch Set 1:    * port the custom lock screen feature from
                  ics (http://review.cyanogenmod.org/#/c/16915)

                * thanks to Danny Baumann, who reworked the
                  framework part to work after Jelly Bean 4.2
                  lockscreen changes

Patch Set 2-3:  * remove obsolete files

Patch Set 4-7:  * revert XML changes

Patch Set 8,9:  * rebased

Patch Set 10:   * fix minor code style

Change-Id: I800506a9f9e001f659ee29b8b2dbe3464e5198f9