Modified mail metadata test so it reproduces encoding issue in resolving mail author:

- Use different names for OGDS user, From: header and To: header.
- Make sure both From: and To: contain non-ASCII characters
- Assert on actual values instead of using the same function the code to
  be tested uses.
Fix UnicodeError in resolving mail author (if author not an OGDS user).
Merge pull request #433 from 4teamwork/lg-fix-unicodeerror-in-resolving-mail-author

Fix UnicodeError in resolving mail author (if author not an OGDS user).