Changed database design to allow multiple proposers per problem/solution.
Rewrote output routines properly.

Write proposers concatenated with "und", using a unified method for
problems and solutions.
Designed and implemented new proposer form.

We can now enter multiple or no proposers, using a dynamic form.
Adapted submit scripts to the new database design.
Allow to distinguish proposers of the same name.

Also: simplified proposers form.
Merge branch 'multprop': resolving issue #9