Move sponsor information from user account to venue ticket

As it turns out, some sponsors are registering the tickets for their
users under a single user account. Therefore, having the sponsor
information on the venue ticket directly makes more sense.
Merge pull request #197 from EuroPython/fix/sponsor-on-ticket

Move sponsor information from user account to venue ticket
Refers #160 -- Add flag to indicate a canceled ticket
Refers #160 -- Only export valid badges
Fixes #160 -- Indicate canceled tickets and prevent modification by user
Merge pull request #198 from EuroPython/fix/ticket160

Fixes #160 -- Allow cancelation of distinct tickets
Always export the status flags if any is given
fixup