[Decision Trees] [UI] Unit tests for Flask server

Summary: Basic tests covering almost all functionality

Test Plan: `make test`

Differential Revision: http://phabricator.tullo.ch/D27
[Decision Trees] [UI] Unit tests and e2e tests for the Angular code

Test Plan: `make test`

Differential Revision: http://phabricator.tullo.ch/D28
[Decision Trees] [UI] Use ngResource for REST backend

Test Plan: `make test`

Differential Revision: http://phabricator.tullo.ch/D29