1.7.2 Prepare framework switch

This is the last release using the old Slim 2 framework that started in 2012 and had its last update in 2017

The next release will jump to version 3.x.x to avoid overlap with:

• the archived @rvolz master and BicBucStriim-352 branches, and
• the updated @mikespub-org backend and frontend branches

which are all suspended unless someone has an interest in working on them further...

Full Changelog: v1.6.6...v1.7.2