Database changes for multicontest
lib.database.php: %Ai now adds the braces itself, so empty arrays are allowed. If an empty array is provided, "(NULL)" will be generated, as this is an "empty list"
Get rid of gewis_ prefix
Fix balloons screen, config checker and add extra data to contest(s) pages (public, short name)
Fix problem(s) screen, use contest shortname in submit client, and fix all API actions using problem data
Fix testcases screen
Add unique index to contest.shortname
Show contest shortname in contest switch dropdown instead of contest ID and name
Update documentation on new tables
Only show publicly available contests in public places (API, /public)
Get rid of contest{team,problem}.php and show contest shortname when adding teams
Added an option to only show the balloons of the currently active contest
Submission: show contest name and link to contest-specific team and problem pages
Clarifications: fix it again and add a switch for showing only clarifications of currently selected contest
Don't need these hidden fields, as cookies take care of them
Fix contest selection at problems + editing problems
Fix problem zip uploading
Show more information in contest table of a problem
Fix problem export
Allow linking of problems to contests