Do not show unimplemented features in production

A few UI elements are displayed without the backing features ready yet:

• Bookmark, both on the preview cards of search results and in the exercise details.
• Show all exercises for this course. This is a collection feature, but we do not support collections yet.
• LaTeX button is rendered for exercises which have the keyword latex, but it is greyed out and not functional.
• Download. Downloading works for me for one exercise ("JUnit Quality Tests Exercise"), but not on any other exercise I tested.
• Views. The number of views works for the exercise "JUnit Quality Tests Exercise" but I could not find any other exercise for which it works.

I assume that the last two issues are related to the visibility of an exercise, since "JUnit Quality Tests Exercise" is the only exercise which is visible without signing in.

changed milestone to %2021 March Sprint Sharing Plattform

mentioned in commit 54dd90fc

Gefixed und gemerged mit !26 (merged) .

Features sind größtenteils noch sichtbar aber disabled und mit Tooltip versehen.

Probleme mit Downloads und Views waren Berechtigungsprobleme.

closed

mentioned in commit f9d846ab