Wrap all yml strings containing "@" with quotes in order to render the
syntax highlighting correctly
Wrap all YAML strings starting with "@" with quotes

Without quotes, the parser doesn't render the syntax highlighting correctly
Wrap all YAML parameter % uses with quotes

Without quotes, the parser doesn't render the syntax highlighting correctly
Remove useless spaces in the YAML code blocks
Merge branch 'yml-rendering' of github.com:lucascourot/symfony-docs into lucascourot-yml-rendering

Conflicts:
	components/dependency_injection/parentservices.rst