IDEF0 support (#1709)

Dear Dusian,

while IDEF1X hast great support by SIM, the process function modelling IDEF0 is not supported.

I use it often with a Visio stencil, which is a break from other SIM models I maintain.

May there be a chance for IDEF0 integration?

Thanks for this awesome software package,

Sebastian

Some references:

http://syque.com/quality_tools/toolbook/IDEF0/how.htm

https://softwaresim.com/blog/getting-started-with-functional-modeling-for-system-specifications/