Added Model Structure Property

Changes:
- Moved metadata/modeling from `StructureProperty` to new `ModelStructureProperty`
- Improved parsing of structure vals to better use the models they are bound to
- Added support for saving nested properties when saving the structure property
- Added customizable "sql_type" to pick among the TEXT data types

src/Charcoal/Property/MapStructureProperty.php

@@ -19,16 +19,4 @@ public function type()
     {
         return 'map-structure';
     }
-
-    /**
-     * Retrieve the property's SQL data type (storage format).
-     *
-     * For a lack of better array support in mysql, data is stored as encoded JSON in a LONGTEXT.
-     *
-     * @return string
-     */
-    public function sqlType()
-    {
-        return 'TEXT';
-    }
 }