[PROPOSAL] Add Fill Holes to Target Cleaning options

[jlampel]

I'd like to add the Mesh / Clean Up / Fill Holes Edit Mode command to the RF Target Cleaning options. Some users have reported missing faces, and that may be due to a previously addressed issue of the face opacity being too low to be obvious if a face is filled or not, but regardless it would certainly be really helpful to have because it's a one click solution.

I think this is one I can tackle, but I'll need to look through how it's done for other Blender commands so that it works with any custom hotkeys or whatnot.