Some PEP8 fixes
Message content for LatexRuntimeException
Don't mix unicode and str when creating ical file
Don't log MaKaCError as unexpected exceptions
Always show exception details for admins
Fix error caused by deleted contribs in author list

Simply skip deleted contributions and authors who have only deleted
contributions (i.e. with no conference assigned)
Fix searching for rooms with equipment
Add maintenance script to fix missing menu links
Don't build system link when editing it

Some links such as eticket download cannot be built without certain
conditions being met (e.g. the current user being registered in the
conference).
Also, the link was just built but not shown anywhere...
Cache PluginOption.getRooms during request
Remove some unused cache utils
Make email body show up properly in log entries
Add seems_html helper to detect MIME in old emails
Prettier WSGI error page
Made NotFoundError a little bit more accessible
Better "not found" messages

Not logged, proper display
Nicer display of service-generated FormValuesErrors
Style fixes, mostly PEP8
Do not propagate conflicts