An ugly solution that allows SMM to use folders

- imports organisation in ManagerFrame
- SMM detects directory structure inside, as well as .ftl files stored
within them, and adds them to its table
- folders can be "opened" by double clicking on the table item
representing them
- on entry, each folder (except for /mods/ directory) creates a dummy
table item that can be used to go back to previouis folder
- in the table, folders that can be entered have a ' >' suffix,
"go-back" dummies have a '< ' prefix
- each folder has its own modorder.txt stored within that folder
- modorder.txt loading/saving is handled on folder entry/exit
- since clearing the table means that information about checkbox
selection is lost, I've moved the selection-remembering functionality
from the TableModel to ModFileInfo
- couldn't find a way to remove the checkbox from folders' table items
-- either way, checkbox doesn't affect folders in any way