Draft: Initial update of the resource management page

This is a bit of a doozy, I spend all day on it and still not done.

TODO:

• Ensure all resources related pages have been covered and aren't duplicating information all over the place.
• this includes the tagging and loading_and_saving_brush_presets pages in the user manual.
• Gradients need updating, which @deiflou said they'd look into. Might be delayed.
• Get RID of any mention of the blacklist files. I am somewhat lost on how we should instruct people on recovering their old brush presets, as we never implemented a UI for versioning.
• Update Screenshots, esp for the new resource manager.
• Improve linking back and forth to the different pages.