The application state was encoded in a QByteArray. Thus, there was
no compile-time checking. Typos would lead to silent failures.
Turn the application state into an enum. Use the enum-class construct,
so that the values don't polute the global namespace. Moreover,
this makes them strongly typed, i.e. they don't auto-convert to
integers.
A disadvantage is that the enums now have to be cast to int
explicitly when used to index an array.
Replace two hash-maps in MainWindow to arrays of fixed sizes.
Move the application-state details into their own files.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>