[Images] A way of clearing the image with `reload_cmd`

[42willow]

Description

Currently if the script/command provides an empty string/path the old path is used, this is a problem if you want to clear the image (eg. when pausing your music and hyprlock is displaying album art)

It would be nice to either change the functionality so that an empty string clears the image, or that specific keywords clear the image (eg. unset or none)

[tbiehn]

It would be cool to turn on and off other visual elements - like shapes - too. Right now I keep a transparent.png and use that to un-set an image as a workaround.