Improve Quick Tour "Big Picture" section and expand Environments docs

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.2+
| Fixed tickets | #2672

* Add a description of environments and front controllers to book/page_creation
* Improve description of the profiler
* Improve the Working with Environments section
* Addresses comments from PR #2683 and targets the 2.2 docs instead of 2.0