[doc] Default group informations

added informations about the Default group in the cookbook
Merge pull request #345 from emilien-puget/patch-1

[doc] Default group informations
Fixes a typo in the annotations.rst
Merge pull request #363 from potherca/patch-1

Fixes a typo in the annotations.rst
Making test running against phpunit 4.*, and fix phpunit version for dev
Merge pull request #369 from joelwurtz/fix/travis-unittest

Making test running against phpunit 4.*
added a GraphNavigatorInterface to allow replacing the GraphNavigator and make the library more extensible.