Support cross-platform importing of PowerPoint presentations using ONLYOFFICE

As a Presenter user, I would like the ability to import PowerPoint presentations from Linux systems. Microsoft PowerPoint is not supported on Linux, but ONLYOFFICE (https://www.onlyoffice.com/) provides a free, cross-platform solution that works on Linux, macOS, and Windows.

This is particularly important because the use of Linux (and not tying software into the need to purchase Microsoft or Apple licenses (or hardware)) is so important for (a) environmental stewardship reasons, and (b) keeping costs down for small churches in poor areas.