Generalized package type for Python packages

[mastersign]

It would be nice to have a generalized package type python-package which installes the package in both Python versions (2 and 3).

[mastersign]

A problem is the automatic dependency which usually activates Python in the required version.

A solution could be, that Python 3 is preferred and only activated, if no Python version is activated explicitly.

[mastersign]

implementation completed in 8444037