[IMP] add rel='nofollow' if nofollow passsed in option of html field, if...

... user have karma more than karma_nofollow then don't add meta tag.

- Task: https://www.odoo.com/web#id=9429&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.VpEnCuXbjsfGEatU
Well it is confusing to have a name that indicates karma for nofollow but do the inverse. Maybe you could rename it to karma_dofollow.