[IMP] [TEST] website_forum: security fixes + tests

- fixed voting, karma check could be avoided
- fixed posting comments, now correctly checking karma (not for
notifications)
- fixed bootstraping of users, now not allowed to ask questions by default;
added validation email that gives the first karma points required to
participate
- added tests
[FIX] remove wrong filter (account)

For some reason, a filter was made on the non-existing field 'categ_id'.
Result: crash crash boom.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64