Add column option, definition in config & adapt form

Exemple for configuration :

```
chill_custom_fields:
    customizables_entities:
        -
            class: Chill\ReportBundle\Entity\Report
            name: ReportEntity
            options:
                summary_fields: {key: abc, form_type: text, form_options: { required: false }}
```

Resources/migrations/Version20150224164531.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Application\Migrations;
+
+use Doctrine\DBAL\Migrations\AbstractMigration;
+use Doctrine\DBAL\Schema\Schema;
+
+/**
+ * Add an option column to customfieldsgroup
+ */
+class Version20150224164531 extends AbstractMigration
+{
+    public function up(Schema $schema)
+    {
+        $this->addSql('ALTER TABLE customfieldsgroup ADD options JSON DEFAULT \'{}\'::json');
+    }
+
+    public function down(Schema $schema)
+    {
+        $this->addSql('ALTER TABLE CustomFieldsGroup DROP options');
+    }
+}