add sidebar for the built-in server in VMs
Remove incoherence between Doctrine and Propel introduction paragraphs
Updated Valid constraint reference

Revised PR #4351 for 2.3 branch
feature #4340 [Cookbook][Web Server] add sidebar for the built-in server in VMs (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[Cookbook][Web Server] add sidebar for the built-in server in VMs

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4149

As discussed with @weaverryan in #4000, this pull request adds a sidebar which explains how to easily use the built-in web server in virtual machines to make it accessible from the host machine.

Commits
-------

28645d9 add sidebar for the built-in server in VMs
[Templating] Added a sentence that explains what a Template Helper is
minor #4344 [Templating] Added a sentence that explains what a Template Helper is (iltar)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4344).

Discussion
----------

[Templating] Added a sentence that explains what a Template Helper is

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | n/a

I found a SecurityHelper in the SecurityBundle. I was unsure what this helper was or what it was supposed to do. After some googling I've landed on the templating component documation. This is correct as the `HelperInterface` can be found in [the component](http://symfony.com/doc/current/components/templating/introduction.html#helpers). However, it doesn't explain what a helper is.

After some searching, [the cookbook *does* explain what a helper is](http://symfony.com/doc/current/cookbook/templating/PHP.html#using-template-helpers). I've pretty much copied over the sentence from the cookbook to the component. If you have a better proposal, I can add that instead.

Commits
-------

6cdecde [Templating] Added a sentence that explains what a Template Helper is
minor #4356 Remove incoherence between Doctrine and Propel introduction paragraphs (arnaugm)

This PR was merged into the 2.3 branch.

Discussion
----------

Remove incoherence between Doctrine and Propel introduction paragraphs

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4349

The introductory paragraph of Doctrine and Propel sections, although both are true in some way, look contradictory, so a rephrase of at least one of the two paragraphs would be convenient.

Commits
-------

7992fdf Remove incoherence between Doctrine and Propel introduction paragraphs
bug #4381 Updated Valid constraint reference (inso)

This PR was merged into the 2.3 branch.

Discussion
----------

Updated Valid constraint reference

| Q              | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3
| Fixed tickets |

Revised PR #4351 for 2.3 branch

Commits
-------

a50bb96 Updated Valid constraint reference
Minor spelling fix
minor #4388 Minor spelling fix (GeertDD)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4388).

Discussion
----------

Minor spelling fix

http://www.oxforddictionaries.com/definition/english/ground

Commits
-------

ef3a58e Minor spelling fix
Merge branch '2.3' into 2.5

* 2.3:
  Minor spelling fix
  [Templating] Added a sentence that explains what a Template Helper is
  Updated Valid constraint reference
  Remove incoherence between Doctrine and Propel introduction paragraphs
  add sidebar for the built-in server in VMs