FooterView color logic cleanup

Bug reports showed that when night mode eneded due to schedule, the text color was updated but not the background color.  Just from analyzing the code, this appears to be due to onConfigurationChanged not being called on the footer view, but NSSL.onUiModeChanged was calling into FooterView.setTextColor.  So logically, this seems like a likely fix, even though I can't repro the bug.

Fixes: 190135611
Test: manual theme change continues to update footer colors.
Test: manual language change updates footer text.
Change-Id: If6fdb527eee244561dcd3975d859de93609662a5