fix python 2.6 build failures

Fixed issue where 'size()' is still used.

Fixed issue where 'size()' is deprecated and still used and prevented making action on multi-choice items.

According to Postgres doc `DECIMAL` is equivalent to `NUMERIC`

DeleteRowAction label

https://www.postgresql.org/docs/9.5/static/datatype-numeric.html

so flask_admin.contrib.sqla.filters.FilterConverter should treat this the same

Fix DeprecationWarning raised by SQLAlchemy

Added missing requirement to TinyMongo example

Added TinyDB - TinyMongo Example.

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