python => python2 in development/ and tests/ and some dev scripts

If you want to run this on debian (which as far as i know is pretty much
the only problematic distribution here), you should be accustomed to the
change necessary by now.
python => python2 in main python files (run_uh and server)

Not including mac setup and build files.
Remove shebangs from files in tests/

Running them directly allegedly doesn't do much.
Merge pull request #2053 from unknown-horizons/python2

python => python2