Design improvements

[mxsph]

The design of the frontend is still very basic and should be adapted. Probably it is the best if we agree on a basic design philosophy and then apply it to everything.

Components/areas that need adjustment

• Adjust title (e.g. digital classroom)
• Adjust favicon
• Adjust conference list (possibly show on a separate page/popover)
• Adjust design of dialogs
• Add tooltips for conference enter/invite buttons
• Remove priority as it can't be changed at the moment anyway? (@snicki13 what do you mean?)
• Adjust the ticket design
• Adjustment of the user list (Since for Avatar upload #19 an avatar should be displayed)
• Style logout.component
• 404 page
• Replace the custom date functions with date-fns (see Design improvements - 1 #73 (comment)).

[snicki13]

The priority is an absurd concept at this moment. Letting students choose the priority of a ticket leads to arbitrary priorities. Perhaps it may be reintroduced later to let instructors assign priorities, when there are multiple tickets in line.

-> Remove priority.