Fix test errors

Pin SQLAlchemy-Continuum to version <1.3.5. This version introduces a bug when unit testing the application. See https://github.com/kvesteri/sqlalchemy-continuum/issues/188 fordetails.

Use http protocol instead of https when mocking with httpretty. Test failed beginning with version 0.9.5 of httpretty and ssl requests. As it is not required to test https, remove it.