Tolerate transactions without other_party/starter
Merge pull request #527 from sharetribe/fix-nil-transaction-person

Tolerate transactions without other_party/starter
Remove auth login from emails but allow unsubscribe.
Update ruby hashes to new format.
Move auth token from global url params to unsubscribe link and update specs.
Unsubribe auth token updated to expire in one week.
Add logging in to features.
Improve readibility by adding line breaks.
Decouple find_user_to_unsubscribe from controller scope.
Combine separate merges into one.
Make auth token more explicit.