Pass a SearchInput object to the back-end
and display the data, which is returned as
a SearchResultDTO.

The previous implementation starting
at testData/, which is in the same directory
as the Java file where the path is used
did not work for me.

This component contains the search input fields.

- Make footer full width and put it at the bottom.
- Replace light blue bar below the navbar
  with white bar, to match the bar above the footer.

Exercise cards are useful in multiple places,
so they should be displayable by an independent
component.

The CSS for making the cards have the correct
width and height is very finicky and took a long
time to get to work. The current styling should
be refactored.

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.

The new search-dropdown component HTML still
includes references to the search component.
Put these in a comment to allow compilation.
Since the component is not in use,
this problem only needs to be addressed if this
dropdown is used in the future.

Make the "Search" button fit in more with
the other navbar items.

Merge remote-tracking branch 'origin/8-umsetzung-der-graphischen-oberflache-von-gernot' into 8-umsetzung-der-graphischen-oberflache-von-gernot

Merge remote-tracking branch 'origin/8-umsetzung-der-graphischen-oberflache-von-gernot' into 8-umsetzung-der-graphischen-oberflache-von-gernot

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