Minor fixes on UI

* Rename namespace to mxp
* Some tests and fixes to render plugins in windows (not by default)

For example, if you want to test user manager as a window instead a tab, you can us e this config:

```
    {
        "ptype": "mxp_usermanager",
        "loginManager": "loginTool",
        "actionTarget":{
          "target": "north.tbar",
          "index": 1
        },
        "outputTarget": null,
        "outputConfig":{
          "width": 800,
          "height": 600
        }
```

in `managerConfig.js`.