Rename pop3s settings to pop3, remove 'insecure'
Fix pop3 SSL state leaking over multisite
Start splitting up methods in Receiver
Use a PostCreator not TopicCreator in email reciever
Add Email::HtmlCleaner for email processing
Restructure HtmlCleaner
Code is correctly parsing all manual tests
Change boundary.eml - same site title
Unflip the order in parse_body
Remove multipart.eml as it didn't make sense

I don't know of any email client that puts the reply in one part and the
original in another part - that seems a bit crazy. The test only worked
because we were choosing the plain-text first.
Rewrite receiver tests
Add InvalidPost tests to Receiver
Give attachment.eml a REAL test
Add a bit of doc to HtmlCleaner