Add more exercise descriptions

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Remove selenium from requirements list, it's no longer used

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Update features page

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Merge

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Update German translations

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Add a link to the exercise overview from the detail page

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Render an icon next to the add comment link on exercise page

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Remove instructions on how to use the search, this is obvious

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Disable the mobile version for now

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Add simple test for the ingredient detail page

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Add tests to check only editors see edit links in exercises app

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Set correct alt-text for icon

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