This PR implements the K7 Login screen, as described in #20015 @ryankeairns @snide @kobelb ## Login form <img width="1310" alt="login" src="https://user-images.githubusercontent.com/3493255/46048123-d9e53d80-c0f5-11e8-9e56-acbe3a8f2b5a.png"> ## Invalid credentials ![image](https://user-images.githubusercontent.com/3493255/46147388-621d2d00-c233-11e8-8a75-beba7bb5a2b2.png) ## Session expired ![image](https://user-images.githubusercontent.com/3493255/46147408-6fd2b280-c233-11e8-97c1-8acb7b2e0c06.png) ## No connection to Elasticsearch ![image](https://user-images.githubusercontent.com/3493255/46147515-adcfd680-c233-11e8-8ad4-3a21d2c06b2c.png) ## Insecure connection ![image](https://user-images.githubusercontent.com/3493255/46147433-8416af80-c233-11e8-82dc-6f32a5ec1bd0.png) Closes #20015