Login hidden in mobile view

[lkiesow]

If you go to https://ai.uos.de in a mobile browser, the page isn't working unless you manage to find the hidden login form. That's unlikely to happen, unless you already know where to look. I'n other words, this probably renders this unusable for most users on mobile:

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[Odrec]

This will be solved in the next commit. The side panel on the start page will be expanded by default