settings: open add tile dialog

Shows the "add tile" dialog QuickSettingsTiles activity when the user press
the add tile button in the system bar

Change-Id: Id416b85aa11cee6fd586ee322650d421ca83cdf0
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
[2/2] Settings: statusbar clock customization + color picker

- added slims clock and date customizations for status bar
- added our own modded marginov color picker which we use as default