Settings: Lockscreen custom wallpaper (2/2)

 - created a listpreference which changes the lockscreen background style
   (eg. Color Fill, Custom Image and default)
 - using the switch the preference for alpha seekbar (custom image only)
   or ColorPreferencePicker switches.

 *** added all necessary colorpicker java files and custom seekbar java

PatchSet 2: fix commit message
PatchSet 3: rebase
PatchSet 4: remove all duplicate files based on what Danesh suggested
PatchSet 5: missed removing the colorpickerpreference I created from
            lockscreen settings
PatchSet 6: fix wrong key for Lockscreen Category
PatchSet 7: Rebase
PatchSet 8: Fix merge conflict
PatchSet 9: Correct strings according to suggestions

Change-Id: I1ac1351e9a31a5827847e30113e933f2b7da219f