[many] Inconsistence between contribution name and associated file max size on database

As it stands, contribution names may be up to 200 characters wide, but associated description, declaration and code filenames only 100. If a user sets a longish name for the contribution (say, with 100 characters), Django will not be able to encode the associated files because their name will superseed the maximum capacity on the database.

We should double the size of the filenames compared to the name. Or halve the first.