SystemUI: Correct settings observer usage

Settings observer was already created by a global variable, but
it was never used and instead a new one was created in start().

Corrected the code to utilize the already created settings observer.

Change-Id: I337ce12bf32f0355f6280f7b74767e5eb17438a6
Signed-off-by: Evan Anderson <evan@thelinuxman.us>
SystemUI: Allow theming of the "no recents" label

This commit defines the label of the "no recent apps" label as a
simple color which allows it to be modified in themes. This resource
matches what CM has been using in cm_colors.xml for a while.

Change-Id: I1346eb25dbcab519f3794d6601337ffa3b632e35

Conflicts:
	packages/SystemUI/res/layout/status_bar_no_recent_apps.xml