Fixing bug with using multiple URL attributes

Updates README.rst with svg badges

Added JSON and JSONB and support for peewee postgresql backend

Allow specifying a primary key field in column_filters (of a peewee ModelView)

fix documentation for flask-login authentication

Don’t initialize index_view twice

Since #1238 was merged, `index_view` would be initialized twice, which
caused the url of an `index_vew` passed in to `Admin.__init__()` not
being read (causing 404s for me 😢). This PR fixes that.

add flake8 test to travis.yml

Add flake8 to tests

use tox, fix mongoengine & python 2.6 tests

add test for column_filters with sqla obj

fix pymongo example ImportError

prevent column_list from being used for details view

use property name rather than db column name for form_choices

Fixes specifying column filter by instance