Add "only show independent mods" checkbox

[burgerhex]

This checkbox goes alongside the "Only show enabled mods" checkbox:

An "independent mod" by my definition is a mod that is not depended upon by any other mods. The use case of this would be users looking to disable any extraneous mods (where "extraneous" means enabled but not used in any capacity). In an ideal world, this feature would be a button like "Disable all unused mods" that magically disables all mods that aren't depended upon by other mods and do not provide maps. In reality, this is probably pretty complicated and not that feasible to implement. The implementation I went with leaves the choice of which mods to disable to the user, but it at least narrows it down to the mods are "safe" to disable.

I would label this as a "major" UI change, since stuff is moving around. As shown in the above image, I moved both checkboxes down to a new row. I am not a UX expert, so I'm not sure what layout would work best here. Open to feedback.

I'm also unsure about the naming "independent mod", since that's somewhat vague. I'm open to any suggestions there, whether that be a new name, or maybe there can be some sort of question mark icon (?) that shows a definition upon hovering.