put error translations in the validators catalog

Symfony searches for validator translations in this particular catalog,
if you put them in your main catalog, error messages won't get
translated.
whitespace
Merge pull request #334 from greg0ire/translation_problem

Translation problem
remove doctypes

Symfony doesn't like them and gives me a 500
Merge pull request #335 from greg0ire/translation_problem

remove doctypes
fix typo in test class name
fix grammar and syntax
Merge pull request #338 from greg0ire/documentation_improvements

Documentation improvements
replace locale with a language

The locale makes the tests fail.
Merge pull request #340 from greg0ire/fix_unit_tests

replace locale with a language
Added datepicker
Merge pull request #341 from Bladrak/datepicker

Added datepicker
Make sure the core bundle is > 2.2.5

This bundle relies on PageableManagerInterface, which is only available
on the master branch of the core bundle. Specifying @dev is not enough
to ensure this. It allows me to install dev-master, but does not force
me to do it, and since I have prefer-stable set to true, Composer
installs 2.2.5, which does not have the interface.