Show login user information

REST API and UI code added for this feature.

REST API Code:
ServerApi.java
ServerResource.java
ServerResourceTest.java

UI code:
index.html
brooklyn.css
home.js


Thankyou for reviewing @sjcorbett !
Just curious, in your eclipse development do you use any formatting config/plugin which does formatting - spacing and indentation with say(Ctrl+Shift+F). Some of the formatting issues looks good in eclipse though not in github. Added four spaces from the beginning and for any code after every bracing.
New review comment changes: https://github.com/bhairavi25/incubator-brooklyn/commit/fc261b70865d045204ad81c80055224b0926174e