Add a theme switcher to the profile settings

Closes #608

See merge request arsnova/cards!1154

fix mongo major version and suspend usage of linux db as it is still empty

Closes #606

See merge request arsnova/cards!1152

Resolve "Improve development with Docker on Windows"

Closes #595

See merge request arsnova/cards!1139

Merge branch '596-play-a-sound-for-answered-correctly-or-incorrectly-when-in-the-learning-phase-of-a-multiple' into 'staging'

Resolve "Play a sound for answered correctly or incorrectly when in the learning phase of a multiple choice quiz"

Closes #596

See merge request arsnova/cards!1138

Merge branch 'staging' into 596-play-a-sound-for-answered-correctly-or-incorrectly-when-in-the-learning-phase-of-a-multiple