Print WARNING and SEVERE log messages in normal mode
Mute INFO-level logging messages in unit tests
Cleaner, typed and persistent store for preferences

This commit introduces a cleaner and typed persistent store for user
preferences based on java.util.prefs.Preferences. It replaces the old one,
that used ugly os-dependent code to find a suitable place to store them.

The store will be persistent across different versions and JAR files, a thing
that the old one didn't guarantee because preferences were stored inside the
JAR itself under Linux.

There is some code duplication in the store, but I am not sure if that can be
avoided.
Compare instructions by serial number

The comparison by binary representation broke some code that tried to find
instructions in a list. Since the new equality relation has way less
interesting properties than the old one, the tests are now superfluous and
thus are removed.
GUICycles refactoring and clean-up

* split business and presentation logic;
* use only english names;
* fix some formatting, remove unneeded variables;
* add convenience methods.
Fix GUICycles window broken visualization

The GUICycles window was broken. Doing a binary search, I found that it has
been broken since I merged the FPU code, and I don't know if the breakage was
already in the code to merge or if I introduced it.

This fix is just am ugly patch, the code that handles this feature is just
too convoluted. If I had infinite time and willpower, I would rewrite it.
However, both my willpower and my time are very limited, so I will just add
this tiny bit of logic that fixes the problems for all the cases that I have
observed.

Automatic testing will be added to detect wrong state transitions during unit
tests; while this does not prove correctness, it will help me to catch
regressions.
Add state validation, that warns if there are illegal states.
Execute GUICycles business logic during tests

It won't make them fail, but warnings will be issued if needed.
Raise illegal state warning to SEVERE, log only SEVERE during tests
Style fixes to make the linter happier
Add the -r command line option

The -r command line option resets the configuration parameters to the default
values.
Fix logic that handles the list of recent files
Add test that runs FPU multiplications

Also, backup and restore the state of the FPU exceptions bits for every test,
and flip them to 0 when needed.
Fix splash screen path