Add a cluster info widget

Should be able to display at least some of the below in some sort of nice way -

```
"build_date": "2015-07-24 10:05:39",
"build_time": 1437732339,
"build_user": "root",
"cluster": "eu-west-1",
"completed_frameworks": [],
"deactivated_slaves": 0,
"elected_time": 1440687155.427,
"start_time": 1440687151.94147,
"unregistered_frameworks": [],
"version": "0.23.0",
"git_sha": "4ce5475346a0abb7ef4b7ffc9836c5836d7c7a66",
"git_tag": "0.23.0",
"hostname": "52.19.160.202",
"id": "20150827-145231-1258422282-5050-1",
"leader": "master@10.0.2.75:5050",
"log_dir": "/var/log/mesos",
"orphan_tasks": [],
"pid": "master@10.0.2.75:5050",
```