Add support for HSTORE columns to SQLA backend

Fix a sample code at introduction

Add a demo app for appengine (and fix one more bug)

Add a basic appengine demo, that can be run with run.sh (assuming appengine SDK is installed). Verifies a few standard NDB/DB Models render well enough.

Fix db.Property index check.

Adds S3 storage backend

SQLA - Use database defaults for number of decimal places in DecimalFields

Renames FileAdmin to BaseFileAdmin and creates a  FileAdmin with a default local storage

add column_display_actions option to ModelView

File admin refactoring to support multiple backends

Fix column filters with translateable column labels.

Update view.py