Adding some early Notifications stubs

* A basic NotificationTemplate model class with early notification type
  definitions
* Initial implementations of the Email, Slack, and Twilio Notification
  backends using the Django email backend system
* Some dependencies thereof

awx/main/notifications/email_backend.py

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+# Copyright (c) 2016 Ansible, Inc.
+# All Rights Reserved.
+
+import logging
+
+from django.core.mail.backends.smtp import EmailBackend
+
+class CustomEmailBackend(EmailBackend):
+
+    init_parameters = ("host", "port", "username", "password",
+                       "use_tls", "use_ssl")

awx/main/notifications/slack_backend.py

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+# Copyright (c) 2016 Ansible, Inc.
+# All Rights Reserved.
+
+import logging
+from slackclient import SlackClient
+
+from django.core.mail.backends.base import BaseEmailBackend
+
+logger = logging.getLogger('awx.main.notifications.slack_backend')
+
+class SlackBackend(BaseEmailBackend):
+
+    init_parameters = ('token',)
+
+    def __init__(self, token, fail_silently=False, **kwargs):
+        super(SlackBackend, self).__init__(fail_silently=fail_silently)
+        self.token = token
+        self.connection = None
+
+    def open(self):
+        if self.connection is not None:
+            return False
+        self.connection = SlackClient(self.token)
+        if not self.connection.rtm_connect():
+            if not self.fail_silently:
+                raise Exception("Slack Notification Token is invalid")
+        return True
+
+    def close(self):
+        if self.connection is None:
+            return
+        self.connection = None
+
+    def send_messages(self, messages):
+        if self.connection is None:
+            self.open()
+        sent_messages = 0
+        for m in messages:
+            try:
+                self.connection.rtm_send_message(m.to, m.body)
+                sent_messages += 1
+            except Exception as e:
+                if not self.fail_silently:
+                    raise
+                logger.error("Exception sending messages: {}".format(e))
+        return sent_messages

awx/main/notifications/twilio_backend.py

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+# Copyright (c) 2016 Ansible, Inc.
+# All Rights Reserved.
+
+import logging
+
+from twilio.rest import TwilioRestClient
+
+from django.core.mail.backends.base import BaseEmailBackend
+
+logger = logging.getLogger('awx.main.notifications.twilio_backend')
+
+class TwilioBackend(BaseEmailBackend):
+
+    init_parameters = ('account_sid', 'account_token', 'from_phone',)
+
+    def __init__(self, account_sid, account_token, from_phone, fail_silently=False, **kwargs):
+        super(TwilioBackend, self).__init__(fail_silently=fail_silently)
+        self.account_sid = account_sid
+        self.account_token = account_token
+        self.from_phone = from_phone
+
+    def send_messages(self, messages):
+        sent_messages = 0
+        try:
+            connection = TwilioRestClient(self.account_sid, self.account_token)
+        except Exception as e:
+            if not self.fail_silently:
+                raise
+            logger.error("Exception connecting to Twilio: {}".format(e))
+
+        for m in messages:
+            try:
+                connection.messages.create(
+                    to=m.to,
+                    from_=self.from_phone,
+                    body=m.body)
+                sent_messages += 1
+            except Exception as e:
+                if not self.fail_silently:
+                    raise
+                logger.error("Exception sending messages: {}".format(e))
+        return sent_messages