JS and CSS clean up based on static code analysis

Thanks to PHPStorm. I actually found a few bugs, but most stuff is
just unused parameters and such.

Change-Id: Ie6e9fc6dc8e0b63d47b3695ec75dcd68f065e06d
Simplify background CSS

PHPUnit's static code analysis complained about this, that's why
I'm touching it. The shortcut property does the exact same. It resets
the background image to none.

Change-Id: I4a7bb046ecc2d3b1df8346c619b274edeec0076d
Merge "Simplify background CSS"
Merge "JS and CSS clean up based on static code analysis"