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

Resources/views/CustomFieldsRendering/number.html.twig

@@ -0,0 +1 @@
+{% if number is not empty %}{{ number|number_format(scale) }} {{ post|default('') }}{% endif %}