add a number field

The field has three option :

- lesser or equal than. If null, this option is ignored ;
- greather or equal than. If null, this options is ignored ;
- precision : the number of decimal after the number ;
- text after the field : a text to show after the field.

The field is rendered as an HTML integer input if precision = 0, or a
symfony number field if precision > 0.

ref chill-project/Chill-CustomFields#11

Form/CustomFieldType.php

@@ -87,6 +87,7 @@ class CustomFieldType extends AbstractType
                 ->buildOptionsForm(
                     $builder
                          ->create('options', null, array('compound' => true))
+                         ->setRequired(false)
                     )
             );
     }