[Python] Massive refactoring - Remove communication via DBus, replaced by KProcess - Supports text result for a python expression with plot image result - Show numpy arrays in full form (because we had solved problem with showing big strings in the variable model) - Use Session::setVariableModel instead of handling variable model by self - Better interrupt - Use expression queue, model updating and expression finishing from Session - Remove unused PythonSession members - Some tests improvments

Closes T6113, T6114
Differential Revision: https://phabricator.kde.org/D21212