Improve usability of report page layout editor

[heralden]

Feedback from Rachel:

The interface is a little confusing but once you know it, it is easy. 1. I’m not sure it is obvious that once you create a category, you then click on that bar to add specifics - although I seemed to find it ok. 2. Once you have added the specific classes, templates etc I didn't realise you had to click the + to actually add them, so I created a report page with nothing on it initially. This is probably me being dim though.