Refactor views to reduce DB use

[meshy]

This is the bulk of the refactor from #175

• Canonical URL is only defined in the templates once, and is calculated more efficiently.
• Views are converted to TemplateViews.
• Django queries within templates are reduced (but not yet eliminated) by doing queries before passing results to the renderer.
• Some careful select_related reduces the number of queries executed.
• Some code is duplicated to keep it encapsulated where it's used.
• The unused module_list.html template is removed.
• Code in dispatch methods is moved into get methods.

Can be reviewed one commit at a time.

Note that while I've kept the mypy ratchet file up to date in this PR, I've opted not to fully address the issues it contains yet.