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
fix typo and move reference to the appropriate file
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
Merge branch '2.2' into 2.3
Update unit_testing.rst

Forget line addExtensions() in example. This line is in FormIntegrationTestCase class. If you don't add this you'll not be able to load additionnal FormType.
Update varnish.rst

fixed missing semicolon
Create block_name.rst.inc
Add block_name entry to the list of form options
Update block_name.rst.inc
[#3008] Minor tweaks to block_name docs
Merge pull request #3028 from xabbuh/date-format-fixes

fix typo and move reference to the appropriate file
Update hidden.rst

typo in label link for inherited options type.
[#3010] Fixing more instances of using the wrong label in some links in form reference section