Merge pull request #125 in ZP/z-push from bugfix/ZP-815-categories-on-emails-are-not-synchronized-updated to develop

* commit '12ea24fc':
  ZP-815 Remove categories if mobile does not submit them.
  ZP-815 Fixed StreamImporter to include categories when streaming an email update, added categories instance variable to SyncMail, added categories to MAPIProvider->GetEmailMapping(), implementing setting categories for emails.

(cherry picked from commit bca74a9c)