net/py-matrix-synapse: Update to 0.18.7

• Add missing run depends
• Add rc script
• Add example configs
• Add instructions to pkg-message
• Add user for daemon to run as non-root
• Add patch to run with newer nacl
• Take maintainership

Approved by: maintainer (private communications)
Differential Revision: https://reviews.freebsd.org/D9228