Cache network requests in homepage & intro views

[tadhg-ohiggins]

Issue #450 resulted in PR #451, which fixed the problem with the days-remaining total, but removing the caching entirely means that the network requests on those pages may result in long load times, particularly if the sites we're requesting from are having any issues.

This issue is to track fixing this by putting caching for those requests into the views, rather than via Django's caching middleware.