Some minor fixes
Change order of annotations to be the same as the gengerator

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | doctrine
| Fixed tickets |
added docs about child forms customization
Updated the documentation for the simplified Callback constraint
CS fixes
Add note about PHP 5.3 behaviour and proxies.
Better wording.
Add a cookbook entry on how to limit session metadata writes
added documentation about Request::setFactory()
added the compact layout information
fix typo and move reference to the appropriate file
Merge pull request #3021 from fabpot/request-factory

added documentation about Request::setFactory()
[#3021] Minor tweaks thanks to @WouterJ and @GromNaN
use literal for class name
Merge pull request #2997 from WouterJ/fix_form_component

Fixes for Form Component chapter
Merge pull request #2998 from youbs/improve_form_customization

added docs about child forms customization
[#2998] Very minor tweaks
Merge pull request #3000 from Urigo/patch-1

Change order of annotations to be the same as the generator
Change order of annotations to be the same as the gengerator

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | doctrine
| Fixed tickets |
Merge branch '2.1' into 2.2

Conflicts:
	components/form/introduction.rst