Theme Engine [4/8]

Squashed Theme Engine related changes.
Added custom lockscreen wallpaper and keyguard changes from cm too.

------------------------------ HISTORY ------------------------------

[+]
Settings: Lockscreen custom wallpaper (2/2)

Hide see throught till we add it as a component for Theme Engine.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>

[+]
Settings: read keyguard package name from overlays

Signed-off-by: Roman Birg <roman@cyngn.com>

[+]
Settings: move keyguard wallpaper to system (2/2)

Change-Id: Id3bb66aa78c2e3dbd1170e74e33fcd160e5a70bb
Signed-off-by: Roman Birg <roman@cyngn.com>

[+]
Add wallpaper pickers to seperate package [2/2]

Change-Id: I233b90aa52b5a8c408fa3adfe3bdad07330cc2ad

[+]
Make LinearColorBar themeable

Move colors to resources and use them instead.

Change-Id: I923e5daa219f302dc24e62faab666483109e6620
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>

[+]
Cleanup