Pythonise and generalise templates

[dandavies99]

Problem: There are lots of templates that are quite similar that could be generalised into blocks that are "included" in individual templates. There are also some aspects of the code that are controlled manually in HTML but could probably be generated programatically, which is more sustainable. E.g. populating the navbar dropdowns.

Proposed solution:

• Review HTML code and see what can be moved to python (e.g. like crispy forms) and what can be generalised.
• Add comments to any blocks of HTML code that are not very basic.

Aha! Link: https://imperial-college-ict.aha.io/requirements/RSE-132-4

[AdrianDAlessandro]

One example was needing to manually add to the template for the filters form at the top of the experiments table template (see change in this PR)