rename src/tgbatest/ltl2tgba

People use this program for doing benchmarks, as if it was meant as a user tool. The problem is that unless you know exactly what algorithms you should chain to obtain your desired output, the output will be crap.

I suggest to rename this tool as spottest to make its intent clear. We then have to adjust all tests that use ../ltl2tgba (but not ../../bin/ltl2tgba!) so they use ../spottest