Convert slime templates to LiveView

[liamwhite]

Slime is unmaintained. The newest release does not compile with the latest version of Elixir and it looks unlikely to be updated ever again.

I have determined the best course of action here is to drop the dependency entirely and move to LiveView templates (which are under the Phoenix framework project umbrella).

To apply this change to a fork:

1. Merge up to commit titled "Add converter"
2. Run mix convert_to_heex and commit the result
3. Run mix format and commit the result
4. Merge the remaining commits
5. Fix any remaining compile errors you encounter

[liamwhite]

I will come back to this once redesign branch is finished