Fix javascript errors when working in a page opened with taget="_blank"
Test content_id with isset instead of a true/false value.

This broke html email in which one image had Content-ID: <0>, which is a
valid value but evaulates to false in this test.
Support IMAP MOVE extension [RFC 6851]
Merge pull request #60 from thijskh/master

Test content_id with isset instead of a true/false value