Law creators should be a many to many

[jorgecarleitao]

Currently, one law has one creator (or None).

Yet, there are inumerous laws that are created by more than one creator (e.g. id=7325, name="Ministérios das Finanças e da Administração Pública e da Economia e da Inovação").

We should have a way to map this name into the different creators, in this case
"Ministério das Finanças", "Ministério da Administração Pública", "Ministério da Economia" and "Ministério da Inovação".

This will require:

1. create a parser to split the name into existing names;
2. modify the crawler to parse the new data correctly;
3. implement a database migration