Add Documents shortcut detection

Summary:
This adds support for Documents detection when included as a default
as implemented in D16852. This is a work-in-progress and currently
does not succeed.

Assistance is welcome.

Test Plan: Run ctest within the dolphin build directory.

Reviewers: #dolphin

Subscribers: elvisangelaccio, kfm-devel, ngraham

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D16967