WIP: big overhaul of developers inspector getViews

It can now show priorities, highlight extensions and overridden views, and show different view types.

- [x] Move [new functionality to new class](https://github.com/Elgg/Elgg/pull/7700#issuecomment-67513533).
- [ ] How to present a list of viewtypes?
- [x] merge with improvements in #7697
- [ ] commit format
- [x] move overrides to the bottom
- [ ] add "view" plugin hook handlers