Anki 2.1.16 Upgrade

Upgrading Anki from 2.0.52 to 2.1.16.

This now requires Python 3 and PytQT5.

Ankiweb stopped support for syncing decks from the legacy 2.0.x versions in January, so for anyone who uses AnkiWeb this upgrade is required.

2.1.16 is about two months old now, but since then they've completely changed their build architecture and added a bunch of new dependencies, possibly including SystemD. I haven't had a chance to experiment with the new build system to figure out if SystemD is actually required, or just an optional extra. If I can't make it work without SystemD this will be the last upgrade to the Anki SlackBuild because I know for myself I'm not going to install SystemD just for some flash-cards.