Some minor fixes
added docs about child forms customization
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
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