Plugin for test pages (again)

This is a follow-up rebased  pull request for #53.

TODO
- [ ] split commits:
    - the ``middlewares.js`` file and associated changes
    - the ``testPage.js`` file and associated changes
    - the dispose process
- [x] refactor ``attester.please.hold`` and ``attester.please.continue`` events, use  [promises](https://github.com/kriskowal/q).
- [ ] attester/attester-doc#1
- [ ] attester/attester-contrib-requirejs#1
- [ ] attester/attester-contrib-noder#2