Remove unused Notifier subclasses, and refactor EmailNotifier into EmailNotificationMixin
Remove unused Notifier subclasses, and refactor EmailNotifier into EmailNotificationMixin

mixxorz/wagtail,gasman/wagtail,takeflight/wagtail,torchbox/wagtail,jnns/wagtail,kaedroho/wagtail,gasman/wagtail,rsalmaso/wagtail,takeflight/wagtail,zerolab/wagtail,takeflight/wagtail,FlipperPA/wagtail,thenewguy/wagtail,wagtail/wagtail,gasman/wagtail,thenewguy/wagtail,kaedroho/wagtail,wagtail/wagtail,FlipperPA/wagtail,kaedroho/wagtail,gasman/wagtail,mixxorz/wagtail,FlipperPA/wagtail,rsalmaso/wagtail,jnns/wagtail,kaedroho/wagtail,zerolab/wagtail,wagtail/wagtail,kaedroho/wagtail,thenewguy/wagtail,jnns/wagtail,mixxorz/wagtail,thenewguy/wagtail,zerolab/wagtail,thenewguy/wagtail,wagtail/wagtail,takeflight/wagtail,rsalmaso/wagtail,wagtail/wagtail,rsalmaso/wagtail,rsalmaso/wagtail,torchbox/wagtail,jnns/wagtail,torchbox/wagtail,zerolab/wagtail,torchbox/wagtail,mixxorz/wagtail,mixxorz/wagtail,FlipperPA/wagtail,zerolab/wagtail,gasman/wagtail