Keep Isso modular, not monolithic. Make it easy to integrate a
web interface or add XMPP notifications.
This refactorization includes minor bugfixes and changes:
* CORS middleware did not work properly due to wrong unit tests
* more type checks on JSON input
* new detection for origin and public url, closes#28
* new activation and delete url (no redirect for old urls, but you can
convert the old urls: copy hash after `/activate/` (or delete) and
open `/id/<id of comment>/activate/<hash>`
* move crypto.py to utils/
With this commit, SMTP is no longer automatically configured: add
`notify = smtp` to the `[general]` section to use SMTP.
