* Add initial version of LineItem Implementation

Signed-off-by: Giovanni Cimolin da Silva <giovannicimolin@gmail.com>

* Adding tests

* Add LTI tests and fix quality isses

* Quality nit

* Add missing requirement, upgrade

* Squash migrations

* Fix merge conflicts

* Addressing review comments

* Add django url testing support

* Add tests to django views, implement compat layer

* Addressing review comments

* Improve tests and test descriptions

* Nit