Check optional metadata fields before
trying to display them.

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.

This button does not fit with the metadata
and took away valuable space in its previous
location.

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

Exchange hard-coded strings for jhiTranslate values.

Metadata still needs to be modified.

Adjust number of cards per row to the screen's width.

Wrap cards into container to achieve spacing
between the cards.

Let all cards in a row have the height of the tallest
card.

IDs need to be refactored further, since
for each search result the same IDs are used.

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

Currently the detail view for a result shows
the information of the first result in the list.