Migrate to using a customized TestRequest

- Have this more closer to z3c.form rather than layers of abstractions
- Similar to what we had before but this is structure independently.
Provide a new mixin for Collection+JSON.

- Verify that the generated template stored also contain the vital keys
  and values.
Split out common functions.

- For better reuse between different mixins.
Implement rendering of submitted values

- This turns out to be a bit more annoying can of worms while I figure
  out how to make it as simple... turns out not so much.