Improve UI/layout code

[alokmenghrajani]

The graphical UI code was an afterthought (the initial design was a command line tool). As a result, the code doesn't use the right design patterns (e.g. there's no MVC). We also place text at fixed offset which only works for a single screen resolution (and assumes the system font is a specific height).

We should consider either:

• improving the layout code to be screen resolution / font agnostic.
• rendering AWT to a frame buffer.
• running X/Wayland and have the Java code be a normal applet.
• some other alternative.

A better UI code would make adding new screens easier (such as backup/export wallet, audit ACLs, etc.)

A related area for improvement is error handling. E.g. making sure we give a clear message if the C code isn't running or if it failed its self checks.