Created Vote, VoteUp and VoteDown domains, and relations with other
domains
Added vote controls :
- user cannot vote if he is not connected
- user (connected) can only vote once for a post (question or answer)
Todo : there is a problem with error messages displayed to the user when
he cannot vote (messages only displayed after refresh of the page (F5))
Tried renders and redirects without success
Merge branch 'master' of
https://github.com/GuillaumeSousa/estouro-de-pilha.git

Conflicts:
	grails-app/domain/fr/isima/estouroDePilha/User.groovy