This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
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