At the moment, we only treat exercises as search results,
but exercises can also appear in other context,
e.g. as bookmarked exercises.

For this reason, it makes more sense to describe them
using the more general term "Exercise".

This is part of an effort to refactor
the large component "MockSearchComponent"
into smaller parts with well defined functionality.

The new component is used for the detail
view of a single exercise.

These errors were ignored by the partial
recompilation of "npm start".
Make sure to recompile to verify that code
actually compiles.

Replace the hard coded paragraph in a search result's
detail view with data taken from the search result.

Previously, the course details always showed data
of the first result. Now, clicking "Open course"
will display the results for the correct course.