Added cookbook page about sessions directory.
Add some clarification to Quick Tour Working with Environments

Also, for the session token: identify what the "weird" hex number is, and and replace "weird" with "long" (a more apt description).
removed duplicate timestamp limitation notice
added timestamp limitation notice for datetime
Merge pull request #2674 from jbafford/i2672

Add some clarification to Quick Tour Working with Environments
Added namespace declaration to MainController.php.
Changed </components/yaml/introduction> to </components/yaml/format> per PR feedback.
Fixed wrong used class
Added article on how to simulate saving locale in session
Added docs for enum nodes
Documented translation.extractor
Documented translation.dumper tag
Merge pull request #2662 from WouterJ/issue_2155

Documented how to simulate old way of saving locale
[#2662] Tweaks to new sticky locale cookbook by @WouterJ

The name was changed only because 2.1 is end-of-life, and I think it's more interesting how to know how to make your locale sticky, and less important that this was the old behavior.
Merge branch 'changing_session_directory' of git://github.com/kevintweber/symfony-docs into kevintweber-changing_session_directory

Conflicts:
	cookbook/session/index.rst
[#2670] Tweaks to new entry about session save path with several tweaks thanks to @WouterJ
Merge pull request #2677 from craue/patch-1

[Form] improve placement of timestamp limitation notices
Merge pull request #2706 from WouterJ/issue_2477

Added docs for enum nodes
[#2706] Very minor tweaks
Merge pull request #2709 from WouterJ/document_translation_dic_tags

Document translation dic tags