[2/2] OmniGears: Lockscreen Notifications

Base: https://gerrit.omnirom.org/#/c/5734/

PS15:
-use our color picker

PS16:
-use our seekbar
-rework some strings

PS20:
- Rebased

Change-Id: I32e3d79a6c7198e66c302d751b50341da6466ff7