folder support

[radiatoryang]

implementation in the sidebar should resemble #3 (comment)

• internally, this is what Yarn Spinner already does... all files get loaded into the same network
• this is pretty important for huge projects with lots of files / scenes / characters
• for earlier discussion, see previous issue #3

work to do:

• need to edit MerinoTreeElement to add two new leaf pseudo-types... a "folder" leaf and a "file" leaf
• add "load folder" button (or let user select multiple folders? need to research Unity Editor's built-in folder picker utility)... sets string[] currentFolders
• a "load folder(s)" method should traverse currentFolders for all subfolders (recursively) and generate the data for the TreeView, will need to modify GetData as appropriate
• a "save folder(s)" method should call SaveData for each item
• should we let users rename folders and files from the sidebar? seems weird to duplicate functionality that's already in the Unity Editor project tab, but I think it's pretty possible

[radiatoryang]

some progress on this... rewriting the file handling / support for multiple files is proving to be a lot of work, it means I have to rewrite file saving as well, and re-think how I'm doing file handling in general... it's lots of fun

[radiatoryang]

lots of progress here... still some loose ends to finish, but the big parts are done