Flesh out tags system + track card languages

[ndepaola]

Description

• This PR expands upon the groundwork laid in #89 in the following ways:
  • The backend continues to come with some pre-configured tags out of the box, but additional tags can be added through the Django admin interface in the Tag table
  • The tagging system now allows tagging folders as well as cards. If you tag a folder, it's implied that everything within that folder (and any child folders) also has that tag.
  • We now track card languages, which must be specified with the 2-letter alpha code at the start of the file - e.g. <EN> card name.png
  • Folders can be marked as containing images of a specific language in the same way they can be tagged
  • The sample cards endpoint filters out NSFW cards
  • Added a UI to the new frontend's search settings for controlling language and tag filters, looks like this:
    • If a filter here is empty, no filtering is applied on that field
  • The detailed view modal displays the card's language and tags
• Keen to hear any feedback before finalising this work
• Will resolve #112

Checklist

• [x] I have installed pre-commit and run the hooks with pre-commit run.
• [ ] I have updated any related tests for code I modified or added new tests where appropriate.
  • Partially but I need to write more tests before shipping this
• [ ] I have updated any relevant documentation or created new documentation where appropriate.
  • On my todo list

[glandu-sr]

Forgot to add that the naming conventions in the Contributors page will need to be updated.

[ndepaola]

To be sure I understand correctly, if I have a folder named <FR>White(NSFW) and a card named Mountain(Artist Name)[Alt], I will have a Mountain card, named Mountain(Artist Name) in the FR language with the tags Nsfw and Alt Art ? Does it just take the direct parent folder or all parent folders ? And what happens if I have and FR folder and put a <DE>Island in it ? Will it be DE or FR ?

Otherwise, great improvements of my tags PR.

the intended behaviour is:

• image-level language specification should supersede folder-level language specification. for example:
  • say you have a folder whose name starts with <FR>
  • within the folder there are two images - one whose name doesn't specify a language, and one whose name starts with <EN>
  • the first image will be classified as French and the second one will be classified as English
• so in your example, the Island would be DE
• it should take the language of the most direct parent language that specifies a folder

upon thinking about it now, i realise my current approach might not capture all of these corner cases - i'll take another look at this code today to double check

thank you for the review btw!