Added empty .py files as placeholders for  retrievability calculator functionality
Merge branch 'master' of https://github.com/leifos/ifind
Merge branch 'master' of https://github.com/leifos/ifind
to resolve conflicts
Merge branch 'master' of https://github.com/leifos/ifind

Update before committing stub code for calculating accessibility functionality.
added stub code for retrievability calculator