opportunity: Creation of a Meetup can now return to its page on error

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
opportunity: Fixed useless null check

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
opportunity: Cosmetic changes to meetup visualization page

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
opportunity: Bugfix for answers at creation of a new attendee for a Meetup

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>