Investigate a switch to Python 3

[GijsTimmers]

Adoption of Python 3 has been slow. Yet, I think that if kotnetcli is portable to Python 3, we should do it. There are some syntax differences, but we can work around that.

We should check if the libraries are Python 3 compatible.

• mechanize: use MechanicalSoup, requests or RoboBrowser instead
• colorama: compatible.
• cursor: compatible.
• keyring: compatible.
• notify2: compatible.
• dialog: compatible.
• beautifulsoup4: compatible.
• argcomplete: compatible.

We can check the Python 3 Wall of Superpowers to find information about other packages.