standard style method names

[rakslice]

Python has an official style: https://www.python.org/dev/peps/pep-0008/

It would be nice if pylaunchy could use plugin method names that fit the standard (https://www.python.org/dev/peps/pep-0008/#function-names). Sorry for the nitpick, but this is an interface and there are people writing plugin code who have python experience who are going to want to follow the standard.

This doesn't need to replace support for the old method names; you could fall back to them for backward compatibility.