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.

Weitere Anpassungen für Login Menu
Including Navigation Menu

authors is no longer a valid keyword.
In this commit the corresponding functionality
is removed. It will be replaced in the future.

keywords was renamed to keyword.
Change some variable names accordingly.
(Some changes might be unnecessary and could be reverted.
I prefer continuing the usage of keywords,
since it is a more logical name for a list of keywords.)

programming_languages was renamed to
programmingLanguage.
Most corresponding variable names have not been changed.

natural_languages is now called language.
This attribute does not seem to be in use.

and additional staging profile