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


Let's disable this test for now. Add it to the 'work in progress' group by changing the annotation to:
```java
@Test(groups = "WIP")
```
And add a comment to the test that says it's disabled because `BrooklynPropertiesSecurityFilter` is not loaded in tests and the server responds 204 No Content.