Add light restore mode

I don't want users to rely on setup priority.

Ref https://github.com/esphome/esphome-docs/pull/248

esphome/components/light/__init__.py

@@ -3,7 +3,7 @@ import esphome.config_validation as cv
 from esphome.components import mqtt, power_supply
 from esphome.const import CONF_COLOR_CORRECT, \
     CONF_DEFAULT_TRANSITION_LENGTH, CONF_EFFECTS, CONF_GAMMA_CORRECT, CONF_ID, \
-    CONF_INTERNAL, CONF_NAME, CONF_MQTT_ID, CONF_POWER_SUPPLY
+    CONF_INTERNAL, CONF_NAME, CONF_MQTT_ID, CONF_POWER_SUPPLY, CONF_RESTORE_MODE
 from esphome.core import coroutine, coroutine_with_priority
 from .automation import light_control_to_code  # noqa
 from .effects import validate_effects, BINARY_EFFECTS, \
@@ -12,9 +12,20 @@ from .types import (  # noqa
     LightState, AddressableLightState, light_ns, LightOutput, AddressableLight)
 
 IS_PLATFORM_COMPONENT = True
+
+LightRestoreMode = light_ns.enum('LightRestoreMode')
+RESTORE_MODES = {
+    'RESTORE_DEFAULT_OFF': LightRestoreMode.LIGHT_RESTORE_DEFAULT_OFF,
+    'RESTORE_DEFAULT_ON': LightRestoreMode.LIGHT_RESTORE_DEFAULT_ON,
+    'ALWAYS_OFF': LightRestoreMode.LIGHT_ALWAYS_OFF,
+    'ALWAYS_ON': LightRestoreMode.LIGHT_ALWAYS_ON,
+}
+
 LIGHT_SCHEMA = cv.MQTT_COMMAND_COMPONENT_SCHEMA.extend({
     cv.GenerateID(): cv.declare_id(LightState),
     cv.OnlyWith(CONF_MQTT_ID, 'mqtt'): cv.declare_id(mqtt.MQTTJSONLightComponent),
+    cv.Optional(CONF_RESTORE_MODE, default='restore_default_off'):
+        cv.enum(RESTORE_MODES, upper=True, space='_'),
 })
 
 BINARY_LIGHT_SCHEMA = LIGHT_SCHEMA.extend({
@@ -41,6 +52,7 @@ ADDRESSABLE_LIGHT_SCHEMA = RGB_LIGHT_SCHEMA.extend({
 
 @coroutine
 def setup_light_core_(light_var, output_var, config):
+    cg.add(light_var.set_restore_mode(config[CONF_RESTORE_MODE]))
     if CONF_INTERNAL in config:
         cg.add(light_var.set_internal(config[CONF_INTERNAL]))
     if CONF_DEFAULT_TRANSITION_LENGTH in config: