Add py-treem

Summary

Add package py-treem. The minimal dependencies are numpy and matplotlib.

Package	py-treem
Contact point	@kozlov
KG entry

Checks

• Software Follows EBRAINS Software Quality Guidelines and reaches level:

  fill the SQ-Checklist.pdf and attach below

• Current maintainer is listed first in package.py
• No pinned dependency versions
• Post-installation tests are defined