mermaid.js uses 70% of transfer bandwidth

[cstaky]

I noticed that on slow connections the theme takes a bit of time to actually show up on a site (up to 5 seconds on a really slow 4G signal). This seemed strange since the theme looks pretty lightweight. Having a look in the Firefox network monitor brought this up:

A 3 MB javascript file in static/ gets loaded on every page that you go on, regardless of whether there is even Mermaid content on that specific page. Granted, it does get cached after the initial GET request, but 3 MB is still a large size for a single js file in static/. Surely there has to be a better way to serve it?, and only on pages were it is required.

Running the demo website (https://not-matthias.github.io/apollo) through some random website analyser confirms the performance issue.

link

cc @rupert648, since you merged this in #82