Enable email-comments

[Dekue]

This program enables comment-replies via email in adhocracy. Features:

• external service
• watch functions: IMAP, Maildir, mbox
• detection of comment duplicates (multiple parsing commands for same email in a fixed time period)
• secure authentication / authorization of user via email address
• parsing of multipart messages (plaintext and html emails)
• parsing of attached images (can only be rendered if markdown's safe_mode is off currently due to usage of data-URIs)
• deletion of (pgp) signatures
• voting
• base frame for sending HTML-emails
• self-explaining and pre-formulated notifications (about new comments) for user; these are in plain text
• test module for parsing; enhanced test-tools: make_comment

[nidico]

Very interesting, thanks for submitting! (There won't be a review from my side in the next 2 weeks due to holidays)