Update book/forms.rst

Fix typo (missing ";") in source code sample for dynamic validation groups
Added final override section
Fixed wrong redirecting
Fixed embedded references
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
[Doc] add link to Varnish website
fix versionadded directive
fix build errors
remove blank line so that the versionadded directive is rendered properly
fix bash command display in components/console/usage
Merge pull request #2990 from WouterJ/override_validation

Added last missing override section