Investigate Django caching

[Pasarus]

Issue raised by: [developer]

What?
Django has many built-in caching solutions that we are not making use of. See here.
There are many areas I believe we could implement caching.

Some examples I have thought of:

• Cache the overview page. Small performance gain, as we will no longer to query for the instruments every time. This cache could have a long expiration time. Template fragment caching could work

• Caching run summaries. It should be possible to cache the run summary page (or a fragment of the template) for each version of a run. This could (potentially) allow the plot to be cached at the same time, allowing a lot of logic to be removed plot_handler

Care must be taken to make sure any logic is not called if a cache is available. It is possible to implement a cache, execute queries, then ignore the result and use the cache. We must avoid that.