Reinstate count from emails.

[rogerhu]

Any reason it was removed? We found it incredibly useful.

[coveralls]

Coverage remained the same when pulling 287df42 on rogerhu:reinstate_count into 646adc4 on getsentry:master.

[dcramer]

The main reason we removed this is because it's quite useless in first-seen emails (its always 1) and it doesnt update dynamically (e.g. something like an image) for regression emails.

i.e. the email is sent now, you view it tomorrow, and its had 100000000 more errors since then, so the count is super inaccurate

[dcramer]

Closing this out for reasons stated