add a custom field long choice basic

The `custom field long choice` aim to provide a way to deal with choices
with a big possibilities.

The `custom field long choice` allow :
- to persist different options in the database ;
- each option has a key, a text (translatable string), and eventually a
  parent, and an internal_key
- every key can be activate or not. If the parent is inactivated, all
  childs are inactivated
- the internal key have two purposes :
    - link to an external csv file, with their own key ;
    - add a special class to results, to allow custom layout.

Currently, the field exists, but some elements are missing :

- a script for CSV import
- possibility to select multiple items
- edition of options
- handle of option without parents
- tests are missing

Resources/config/doctrine/CustomFieldLongChoice.Option.orm.yml

@@ -0,0 +1,33 @@
+Chill\CustomFieldsBundle\Entity\CustomFieldLongChoice\Option:
+    type: entity
+    table: custom_field_long_choice_options
+    repositoryClass: Chill\CustomFieldsBundle\EntityRepository\CustomFieldLongChoice\OptionRepository
+    id:
+        id:
+            type: integer
+            id: true
+            generator: 
+                strategy: AUTO
+    fields:
+        key:
+            type: string
+            length: 15
+        text:
+            type: json_array
+        internalKey:
+            type: string
+            length: 50
+            column: internal_key
+        active:
+            type: boolean
+            default: true
+    oneToMany:
+        children:
+            targetEntity: Chill\CustomFieldsBundle\Entity\CustomFieldLongChoice\Option
+            mappedBy: parent
+    manyToOne:
+        parent:
+            targetEntity: Chill\CustomFieldsBundle\Entity\CustomFieldLongChoice\Option
+            inversedBy: children
+            nullable: true
+