Config file (markdown?) for introduction and page ordering

[bvreede]

The order of cards on the landing page seems somewhat random at this point. We want to make this explicit, but it would be good to not hide the order somewhere in the depths of a .vue or .html page. Instead, perhaps we can create a config file which can be used by the index.html/index.vue page to check the order of different cards.

This config file can also be used as the source for an introductory text on the main page.

[bvreede]

As of #27, the order of subjects is hardcoded in pages/index.vue. It should be in a config file.