ims_lti_py is broken and abandoned

[e-kolpakov]

This app uses ims_lti_py to receive, parse, build and send LTI requests. Unfortunately, ims_lti_py seems abandoned, as PyPi version haven't been updated for some time there's an issue abut that. This complicates deployment, as django_lti_tool_provider can't be properly installed using only setup.py, hence if included into other package requirements.txt it will fail the setup (or install broken ims_lti_py version).

[e-kolpakov]

Probably we should migrate this to https://github.com/pylti/lti