Core API module change plus general improvements and fixes

Quite of a lot of changes and updates, but to be fair it's been a while since the last release...

• Changed the core API dependency module from python-qbittorrent to qbittorrent-api as the latter is being updated regularly
• Fixed a loss of communication between HA and the qBitorrent client never being retried
• Added a new action: delete_torrent
• Enhanced the existing get_torrent_info action with a new state_filter option
• General code tidy-up
• All the actions now have icons in the Developer page actions picker!

I think there's still some work to be done when experiencing a loss of communication as right now each sensor is going through the timeout/unavailable process, rather than it being done at the device level.

Please let me know if you experience any issues with this update of course.