APY-120 : Add support for mongoengine

Sample content item with mongoengine.
APY-120 : Add support for mongoengine

Added validation and also more item samples
APY-121 : Polymorphic support for models

Small updates for polymorphic testing.
APY-112: Make authentication user name case insensitive

converted to lowercase before comparing
APY-47: Refactor CDM to include content metadata and make it extensible

added metadata for publishing images
cleanup
APY-112: Make authentication user name case insensitive

added str.lower instead of sqlalchemy lower func (review comments)
Merge pull request #526 from cristidomsa/auth

APY-47: Refactor CDM, APY-112: Make authentication user name case insensitive
Merge pull request #525 from mihaigociu/apy-8-implement-x-filter

Integrate UI with the refactored REST API
Fixed MetaInfo bug
Work on APY-118 Migrate media archive screen to the new REST API