[DDC-2160] Smart Pluralize/Singularize support for Doctrine/Common/Util/Inflector

Doctrine/ORM/Tools/EntityGenerator should pluralize/signularize correctly.

This PR adds functionality to Doctrine/Common/Util/Inflector to singularize/pluralize. The code is largely borrowed from a similar class in the CakePHP project - I'm not sure if the updates to the class doc covers the requirements for this.

Test coverage also added.