Refactor build process

[marvinmarnold]

Problems to address:

• PyGObject is not heavily used but introduces a dependency that is a PITA. It takes forever to build with pip and we have not been able to get it working using the system installs.
• Removing venv. This was prevented previously because PyGObject would complain after venv removed:

Traceback (most recent call last):
  File "/opt/lib/cputemp/service.py", line 30, in <module>
    from gi.repository import GObject
  File "/usr/lib/python3/dist-packages/gi/__init__.py", line 42, in <module>
    from . import _gi
ImportError: cannot import name '_gi' from partially initialized module 'gi' (most likely due to a circular import) (/usr/lib/python3/dist-packages/gi/__init__.py)

• Unpinning package versions. This was last attempted at the same time as other changes and likely contributed to the issues.

[shawaj]

Related to #127