Show calculation by PIDs

refactor the path routing, see below
add an API endpoint that resolves PIDs

The path routing should work with the following paths

/gui/search
/gui/dataset/doi/<doi>
/gui/dataset/pid/<pid>
/gui/entry/pid/<pid>
/gui/entry/id/<upload_id>/<calc_id>

Edited Sep 03, 2019 by Markus Scheidgen