Add file choosers

[pfroud]

The user can use GUI buttons to choose a KSY file and a binary file. The KSY file is compiled in a background thread, and a status bar shows the progress.

I also stole the favicon from kaitai.io to use as the application icon. Screenshot of new GUI items:

Notable code refactoring changes:

• Narrow the Java generic types.
• Move Swing method calls to the Swing Event Dispatch Thread.

Additions to README.md:

• Add a screenshot.
• Add instructions about how to launch the application, in response to this comment on an issue: Cannot open any files #10 (comment)