Small UI Improvements (0.19.0 Alpha)

Most of this release was about changes to make it easier for me to build user interface code in the future.  I also fixed an irritating bug in the user interface (keys causing beeps while typing in a load/save dialog box) and added a little dialog box that gives a small statistical report on the current world.  This can be accessed from the 'World' menu.

When generating a random world, you can now specify the seed.  Along with the new dialog box, which can tell you the seed value for a world, this allows you to generate an unmodified world identical to a previous world.

Here's the new dialog box: