Feature/131 jobref nodefilter

for #131 

Job references can override the Node Filter, Threadcount and Keepgoing for the referenced Job.

Form GUI:

![screen shot 2014-11-17 at 4 01 45 pm](https://cloud.githubusercontent.com/assets/55603/5080435/c4d9a48a-6e74-11e4-87d7-ac595f23cc68.png)

Current format in Job XML:
```{.xml}
<command>
        <jobref name='some job'>
          <nodeFilter>node1 node2</nodeFilter>
          <nodeThreadcount>2</nodeThreadcount>
          <nodeKeepgoing>true</nodeKeepgoing>
          <arg line='-opt blah' />
        </jobref>
</command>
```

Current format in Job Yaml:

```{.yaml}

    - jobref:
        group: ''
        name: some job
        args: -opt blah
        nodeFilter: node1 node2
        nodeThreadcount: 2
        nodeKeepgoing: true
```