IMAP support in EmailUtil

I know i've mentioned it before, and this was rejected. But i don't remember why, and as days
pass by, I have to plan for more and more deployments of qa monitors, and there are too many
manual steps involved.

In our setup, we have to create as many email accounts as we have distinct logical
tests the moment they could run in parallel:

availability1.<somedomain>
availability2.<somedomain>
...
availability70.<somedomain>

This is too much overhead in terms of DNS configuration + Unix account management + Postfix account management.

This is due to TestPlan only supporting POP3.

With support for IMAP, we'd be able to create a folder structure that mirrors the logical structure
of our test hierarchy:

Setup I want to arrive at:

0. One wildcard email domain delivers to...
1. One unix account with procmail / dropmail / sieve which moves the file (based on domain name, example loginplus.set1.<domain>) to ...
2. Maildir/INBOX.* subdirectory (example: Maildir/INBOX.set1.loginplus)
3. Test cases are configured with

 %Email.Pool.Port% (inherited from shared config)
 %Email.Pool.Host% (inherited from shared config)
 %Email.Pool.User% (inherited from shared config)
 %Email.Pool.Pass% (inherited from shared config)
 %Email.Pool.Folder% (specified by the test, example: '/INBOX.set1.loginplus')

4. Test cases only look in the folder they're meant to for incoming messages
5. Everyone is happy (SysAdmin + QA department), because there is now no manual step
in configuring the unix account of the postfix configuration.

({Issue:38689} in our internal issue tracking system)