Keeps track of unsuccessful authentication attempts via an int counter
in the state struct. Displays on the unlock indicator, but will be
replaced by the Caps Lock text if enabled.
The -c/--color option no longer sets BACKGROUND_MODE_SOLID_COLOR (which
disables the background image) and the background color is now set in
all cases. One can still use --scaling solid_color to disable display of
a background image.
As a consequence, there is now only one possible default background
colour (white), regardless of whether a background image is given or not.
This implements customization for the indicator as proposed in sway#2788 with comments from sway#3367 in mind.
The default behaviour does not change exept for the caps lock text color.
Since these changes seem to be lost in the split I've remade them.
