fix-issue1602-peewee-basemodel

This fixes issue described in 1602 and 1606 where the Peewee ORM changed their function for BaseModel to ModelBase in Peewee 3.0 and greater. This should work for Peewee versions less than 3.0 as well.

flask_admin/contrib/peewee/form.py

 from wtforms import fields
 
 from peewee import (CharField, DateTimeField, DateField, TimeField,
-                    PrimaryKeyField, ForeignKeyField, BaseModel)
+                    PrimaryKeyField, ForeignKeyField)
+
+# Fix for Issue: #1602 & #1606 
+# Section below trys BaseModel (for versions of PeeWee < 3.0) and if that fails,
+# load the new ModelBase as BaseModel (to not break things looking for BaseModel in flask-peewee and etc.)
+
+try:
+    from peewee import BaseModel
+except ImportError:
+    from peewee import ModelBase as BaseModel
 
 from wtfpeewee.orm import ModelConverter, model_form