config: reduce default statusline height slightly (to 24px)
widgets: add magick_background widget for blur/desaturate background effect
widgets/magick: update default values and function calls

Fatal flaw with config system found: integers that are zero in the config
file can't override default integers. This needs to be fixed.
Fix issue with widget init macros

Previously 0 (zero) integers and reals in config.json would not override
the default values in the config structs if the default values were != 0.

This update adds some extra checks for undefined (NULL) config properties
and overrides the default values correctly even if the property is zero.
widgets/magick: switch from imagemagick to graphicsmagick

The performance is *a lot* better with graphicsmagick, and the API
is very similar. Could possibly support both at some point in the future.
widgets/magick: update default values