ROIs right_plugin uses .omeroweb_right_plugin()

Improve the example of using right plugin by using the jQuery plugin to add this to the right panel.

To test (locally), uncomment this line in omeroweb/settings.py

```
#'["ROIs", "webtest/webclient_plugins/right_plugin.rois.js.html", "image_roi_tab"],'\
```
When web restarts, check that the ROI tab has been added to the right tab and that it is only active when an Image is selected. 
When you click the tab it will show any ROIs in the image as preview images.