Supporting Multiple World Directories

With this, I envision a system in which the path for multiple world directories and individual worlds can be saved. With this, all the worlds can be compiled and displayed like they currently are, or there could be a tab like system to change between different directories. This would minimize time spent crawling through directories going back and forth between directories.

Edit: A system for saving scenes would be required for #315 to be implemented anyway.

Start by reviewing how the application currently discovers and displays world directories, then read issue #315 for the related scene-saving requirement. Done means users can save multiple world-directory and individual-world paths, compile and display all worlds, and switch between directories through a tab-like interface.

Written by the indexing model from the issue text.