qBit tag support

[masonfox]

Allow users the ability to apply tags to their selection:

• Can configure what tags are available
• Can configure a default tag for each medium: book and audiobook
• List view and dual-mode have tag selection support, but default to their respective defaults
• There's a new page to manage your tags. A new settings is probably fine
• On the settings page, you can configure whether to enable tags or categories, turning them on or off. They're both off by default.
  • We continue to default to "audiobook" and "books" for categories, though

[masonfox]

Update here! I had made substantial progress on this feature... But, in the midst of hastily moving to another Linux distro, I failed to realize that I hadn't pushed up my local branch for this feature... Alas, it was lost 😢

Therefore, I'll need to start over!