FEATURE: context is not emailed if we previously emailed you the post
FEATURE: site setting to enable_watch_new_topics , false by default.
When enables users can elect to watch everything by default
FIX: Custom email subjects (x quoted you in [title], x replied to [title])
was removed, this broke email grouping. TBD, include info in footer somehow
FIX: topic user specs were messy, reduce side effects
