Merge branch 'amiranda/109-use-mochi-thallium-instead-of-our-custom-margo-engine' into 'main'

Resolve "Use mochi-thallium instead of our custom Margo engine"

This MR removes our in-house C++ engine for Margo and replaces it with 
mochi-thallium. This makes code simpler since the daemon implementation can 
be fully in C++, which prevents having to muck with C types and their 
lifetimes.

Closes #109

See merge request !74