Revert "Merge branch 'fix-email-threading' into 'master'"

This reverts commit 97fd990ecde387290be269ef7daafa5761f94af6, reversing
changes made to f451a697e0c018359e6d8ff3aaba4eb0484c4bee.

Conflicts:
	app/mailers/emails/notes.rb
	app/mailers/emails/projects.rb
Merge branch 'revert_email_thread' into 'master'

Revert email threading rewrite

The 'to:' address introduced by this merge caused a flood of email going to an admin account for GitLab.com. This feature should not be shipped as-is.
Fix project trasnfer for admin area

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'fix-500-admin-transfer' into 'master'

Fix 500 error when transfer project from admin area

Fixes #1349