Add logo to the community.

def addlogo(community_id, logo):
    """Add logo to the community."""
    # Create the bucket
    c = Community.get(community_id)
    if not c:
        click.secho('Community {0} does not exist.'.format(community_id),
                    fg='red')
        return
    ext = save_and_validate_logo(logo, logo.name, c.id)
    c.logo_ext = ext
    db.session.commit()