Added observers to watch model objects for mail delivery instead of calling Mailer.

Added observers to watch model objects for mail delivery instead of calling Mailer.

* Added an IssueObserver to watch when Issues are created
* Added a JournalObserver to watch when Journals are created (Issue updates)
* Added a NewsObserver for News items.
* Added a DocumentObserver for Document notifications.
* Setup IssuesController#new to use the IssueObserver.
* Setup IssuesController#edit to use the IssueObserver.
* Setup IssuesController#bulk_edit to use the JournalObserver.
* Removed the Mailer call in Changeset#scan_commit_for_issue_ids, the
  JournalObserver will handle it.
* Removed Mailer calls in MailHandler in favor of the Observers.

  #2659

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2637 e93f8b46-1217-0410-a6f0-8f06a7374b81