Added user avatar to header
## What does this MR do?
Adds the users avatar to the header with a dropdown for profile & sign out.
## What are the relevant issue numbers?
Closes#18543
## Screenshots (if relevant)
![Screen_Shot_2016-06-27_at_12.47.34](/uploads/852d0eb7075eefcf21f5cf5ff71a389a/Screen_Shot_2016-06-27_at_12.47.34.png)
![Screen_Shot_2016-06-27_at_12.47.36](/uploads/6cb29843d3a12bbf2d3ed2a7c9bde770/Screen_Shot_2016-06-27_at_12.47.36.png)
See merge request !4939