Drop pyramid_deform and horus HTML views

Close #1552
Merge pull request #1569 from hypothesis/1552-fully-integrated-auth

Drop pyramid_deform and horus HTML views.
Move notification to a separate directory
Add includeme()
DeOOP Notification templates

ReplyTemplate and NotifierTemplates were semi-classes with only a bunch of
static functions collected under a class. Separating the templates in module level
makes these abominations obsolete.
Create reply-notification for newly registered users
Move domain_mailer into notifications
Notifications tab stub