Migrate project to python3.x

[KrzysztofGrzempa]

I belive migrating code to python3.x is one of the first thing, that has to be done, before any other improvements can happen.

[ronys]

Indeed. I've started this in the 2to3 branch, but abandoned the effort for now, for reasons described in the README.md in that branch.
In any case, the main project (https://github.com/pwsafe/pwsafe) now has a command-line interface (pwsafe-cli), which users of this code might find useful.