imap: Added the ability to FETCH a specific UID and SECTION

Updated the FETCH command to send the UID and SECTION parsed from the
URL. By default the BODY specifier doesn't include a section, BODY[] is
now sent whereas BODY[TEXT] was previously sent. In my opinion
retrieving just the message text is rarely useful when dealing with
emails, as the headers are required for example, so that functionality
is not retained. In can however be simulated by adding SECTION=TEXT to
the URL.

Also updated test801 and test1321 due to the BODY change.