feat(BetterFolders): add folder nesting & multi-column mode.

[wagyourtail]

I have implemented 2 new modes for better folders.
the first simply makes each folder open in its own column (obviously this one won't do anything if closeOthers is enabled):

this was merely created as a stepping stone to implementing the other mode, but I realize some people may want it

and the nested mode actually implements a tree-like structure:

for the nest mode, folders are simply parsed by name and split on /, so on an unmodified client, the folders would simply be displayed next to eachother.
there is currently a limitation that a parent-folder has to exist for the nest to actually nest