Reorganize and expand quickstart big picture docs on environments

* Add Environments section under "Understanding the Fundamentals" to introduce environments. This uses the glossary definition as a starting point and expands on it a little.
* Move the Web Profiler discussion out of Working with Environments into a separate section, and add a paragraph briefly summarizing what the profiler can do.
* Improve the Working with Environments section.
* Original changes from PR #2683 rebased on 2.2
remove remaining references to the virtual option
added empty_value
Add submit buttons to form building examples
Big Picture Environments cleanups

* Move the environments and front controller discussions to book/page_creation
* This allows for the debug toolbar discussion to be more prominent
Removing duplicate content

The same content can be found at the end of the "Configuration and setup" section. I've removed the more recent content, and because I think the right place is in the "configuration" section.
fixed external link to form_div_layout.html.twig from 2.2 to 2.3
Changes for correctness
Fix typo
Merge pull request #2808 from xabbuh/issue-2802

remove remaining references to the virtual option
Update service_container_parameters.rst
better grammar
a bit of indentation
moving reference from debugging to templating formats to fix problem with note giving wrong link
clarification difference between function and tag includes
update according to stofs comments
[#2813] Tweaks to explaining how variables are passed into included templates and making references to older include tag easier to get more information about
Merge pull request #2816 from Nyholm/patch-1

Missing field in documentation: Added empty_value
EventDispatch implements the Mediator pattern, not the Observer pattern
Merge remote-tracking branch 'origin/2.2' into 2.2