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