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