Added an option to disable Locale listener

Hi,

In some case, using the Symfony2 locale (for example from the Request) to automatically filter entities using the `Translatable` extension can lead to unwanted results.
I came across such case in an application where the locale was already managed explicitly.

In this PR, we create an optional `disable_locale_listener` option. The default value is `true`, so there are no  BC break.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | ~
| Fixed tickets | ~
| License       | MIT
| Doc PR        | Doc written
``~`` means ``null`` in YAML, which does not make sense for a boolean node