1.1.3dev: Split up notification module. (see #11854)
* `api.py` contains interface definitions and the `NotificationSystem`
* `mail.py` contains email specific functionality
* `compat.py` contains base classes to be deprecated and removed later
* `__init__.py` contains imports for backwards compatibility

Also fixed import of `BatchTicketNotifyEmail` in `trac/ticket/roadmap.py`.

And extracted some reusable mail helpers from `NotifyEmail` and `TicketNotifyEmail`:
* `create_charset`
* `create_mime_text`
* `create_header`
* `create_message_id`
* `RecipientMatcher` (handles config options `admit_domains`, `ignore_domains`, `use_short_addr` and `smtp_default_domain`)


git-svn-id: http://trac.edgewall.org/intertrac/log:/trunk@13433 af82e41b-90c4-0310-8c96-b1721e28e2e2