Fixed 'new world' dialog to allow the selecting of pre-existing resource
packs, and to disable browse and text fields when 'use default pack' is
selected, making the dialog finally usable.

Began porting 'In The Swing'. The complexity of the level is higher than
Spooked; it will take more time to port.
In the Swing world accidentally not added to last commit
Forgot bee, and bonus/exit door in In The Swing resource pack.
Corrected a resource pack issue with a missing pattern and added a few
more screens to In The Swing
Done with In The Swing. Need to both play-test and fix an issue
preventing a choice in which side a two-way sprite should face (which is
very prevalent in the bees in this level)
Palette Swapped the conveyer belts; wrong colours were used from
original for the directions.
Made final touchups to the world. World is beatable.
Fixes #12
Updated .jar