Improved search for the UPPAAL verifyta executable: now we first try to
find it in a directory whose name contains "uppaal" (lowercase
comparison), which considerably speeds up the search. Only if that fails
we do a bruteforce search everywhere for a file named "verifyta".
Also, when starting ANIMO we check that the path to verifyta is still
existing, and in case we do again the automatic search + possible user
input to find it.