Imap sensor (#2485)

* Imap unread email sensor

Checks the inbox of a imap account for unread emails. Tested against
gmail.

Example config:

```
sensor:
  - platform: imap
    name: gmail test
    user: USER
    password: PASSWORD
    server: imap.gmail.com
    port: 993

```

* added to .coveragerc

* Code cleanup and typo fix.

* Added port range validation

* Fix lint errors

.coveragerc

@@ -191,6 +191,7 @@ omit =
     homeassistant/components/sensor/glances.py
     homeassistant/components/sensor/google_travel_time.py
     homeassistant/components/sensor/gtfs.py
+    homeassistant/components/sensor/imap.py
     homeassistant/components/sensor/lastfm.py
     homeassistant/components/sensor/loopenergy.py
     homeassistant/components/sensor/neurio_energy.py

homeassistant/components/sensor/imap.py

@@ -0,0 +1,104 @@
+"""
+Imap sensor support.
+
+Checks an email account for unread emails.
+"""
+import logging
+import voluptuous as vol
+
+from homeassistant.helpers.entity import Entity
+import homeassistant.helpers.config_validation as cv
+
+_LOGGER = logging.getLogger(__name__)
+
+ICON = 'mdi:email-outline'
+
+CONF_USER = "user"
+CONF_PASSWORD = "password"
+CONF_SERVER = "server"
+CONF_PORT = "port"
+CONF_NAME = "name"
+
+DEFAULT_PORT = 993
+
+PLATFORM_SCHEMA = vol.Schema({
+    vol.Required('platform'): 'imap',
+    vol.Optional(CONF_NAME): cv.string,
+    vol.Required(CONF_USER): cv.string,
+    vol.Required(CONF_PASSWORD): cv.string,
+    vol.Required(CONF_SERVER): cv.string,
+    vol.Optional(CONF_PORT, default=DEFAULT_PORT):
+        vol.All(vol.Coerce(int), vol.Range(min=1, max=65535)),
+})
+
+
+def setup_platform(hass, config, add_devices, discovery_info=None):
+    """Setup the IMAP platform."""
+    sensor = ImapSensor(config.get(CONF_NAME, None),
+                        config.get(CONF_USER),
+                        config.get(CONF_PASSWORD),
+                        config.get(CONF_SERVER),
+                        config.get(CONF_PORT, DEFAULT_PORT))
+
+    if sensor.connection:
+        add_devices([sensor])
+    else:
+        return False
+
+
+class ImapSensor(Entity):
+    """IMAP sensor class."""
+
+    # pylint: disable=too-many-arguments
+    def __init__(self, name, user, password, server, port):
+        """Initialize the sensor."""
+        self._name = name or user
+        self._user = user
+        self._password = password
+        self._server = server
+        self._port = port
+        self._unread_count = 0
+        self.connection = self._login()
+        self.update()
+
+    def _login(self):
+        """Login and return a imap connection."""
+        import imaplib
+        try:
+            connection = imaplib.IMAP4_SSL(self._server, self._port)
+            connection.login(self._user, self._password)
+            return connection
+        except imaplib.IMAP4.error:
+            _LOGGER.error("Failed to login to %s.", self._server)
+            return False
+
+    @property
+    def name(self):
+        """Return the name of the sensor."""
+        return self._name
+
+    @property
+    def state(self):
+        """Return the number of unread emails."""
+        return self._unread_count
+
+    def update(self):
+        """Check the number of unread emails."""
+        import imaplib
+        try:
+            self.connection.select()
+            self._unread_count = len(self.connection.search(
+                None, 'UnSeen')[1][0].split())
+        except imaplib.IMAP4.abort:
+            _LOGGER.info("Connection to %s lost, attempting to reconnect",
+                         self._server)
+            try:
+                self._login()
+                self.update()
+            except imaplib.IMAP4.error:
+                _LOGGER.error("Failed to reconnect.")
+
+    @property
+    def icon(self):
+        """Return the icon to use in the frontend."""
+        return ICON