FEAT: Create a new section for Groups on homepage

The Groups are a way to assemble people with same skills or interests and allow them to interact.

Just like Chats :

• The connected User can see the Groups they're in
• When they enter a Group, they see a Chat where all the members of a group are present
  • Whenever a User is added to a Group they are also added to the related Chat (this will also work when a new group is created and the first user is added to it, use doctrine listener on Group entity)