Moved formatOnWrite function to Bookshelf override plugin

no issue

- `formatOnWrite` doesn't override anything in Bookshelf but we use it
  within the `override` plugin and sub-models may override it, so it's
  easier to keep these things together

core/server/models/base/index.js

@@ -47,11 +47,6 @@ ghostBookshelf.Model = ghostBookshelf.Model.extend({
         proto.initialize.call(this);
     },
 
-    // overridable function for models to format attrs only when saving to db
-    formatOnWrite: function formatOnWrite(attrs) {
-        return attrs;
-    },
-
     hasDateChanged: function (attr) {
         return moment(this.get(attr)).diff(moment(this.previous(attr))) !== 0;
     },

core/server/models/base/plugins/overrides.js

@@ -33,6 +33,13 @@ module.exports = function (Bookshelf) {
             return parentSync;
         },
 
+        // overridable function for models to format attrs only when saving to db
+        // this function doesn't override anything in Bookshelf but we use this in
+        // this plugin and sub-models may override it, so it's easier to keep it in here
+        formatOnWrite: function formatOnWrite(attrs) {
+            return attrs;
+        },
+
         // format date before writing to DB, bools work
         format: function format(attrs) {
             return this.fixDatesWhenSave(attrs);