GUI initial revision, among other things

[mkacct]

Primary changes:

• The first revision of the GUI is now implemented and tested (the framework-independent part is tested)
• Application behavior shared between CLI and GUI extracted to new class domain.CheckUtil

Minor changes:

• New class ProductInfo has name and version constants
• CLI now prints version info
• JsonFileConfigLoader throws the right kind of exception
• Renamed directory cli-system-test to just system-test since it is also used by GUI system test now

Things that were not yet developed:

• The GUI settings page is NYI; the GUI cannot write config yet