Add car + non-table inline edit tests

Related to this PR : https://github.com/sonata-project/SonataDoctrineORMAdminBundle/pull/302

In order to add a non-table inline edit field, I created a new "Inspection" entity, containing a date field. A car can have many inspections.

The car "getNewInstance()" method automatically add an Inspection as we can click the Add button without javascript enabled (as far as I know).

Moreover, I added some tests to the car entity.