Adding the actual job description and job name to graph if set

This is a small adaptation to the Build Flow Plugin graph. It adds the actual job description and job name if this is set. Only the jelly-script is updated.

Using this script:
build.setDescription("My flow description")
build.setDisplayName("MyName")

test1 = build("Test1").build
test1.setDescription("Description set by user")
test1.setDisplayName("NameMe")
test1.setDescription()

test2 = build("Test2").build
test2.setDescription("Description set by user")
test2.setDisplayName("NameMe")
test2.setDisplayName()

build("Test1").build

Will create the following graph:
![build_flow_naming](https://f.cloud.github.com/assets/4181469/430087/0fd03a0a-ae5d-11e2-819d-ab9333e5a6ac.png)