Add GUI tests to CI pipeline (Janek). Fix issue #120 (Bruno)

OK, this is working now very nicely:

• GUI crashing works
• gdb backtrace works
• id==-1 fixed temporarily in 9e02d455, we will revert this commit once we find a real fix.
• !301 (merged) fix works.

We can see backtraces:

• without id==-1 fix
• with id==-1 fix, without !301
• and all works with !301