Fix pacgraph-tk regression for Python 3.12

[ekorchmar]

Fixes issue #12.

Backstory

CPython's imp module was considered deprecated since 3.4, and was completely removed at 3.12; importlib should be used instead. As of right now, Python 3.12 is the default Arch package, so pacgraph-tk is de facto broken out of the box.

Relevant links

• Python version in Arch (3.12.3 now)
• imp docs -- note the deprecation notice.

Changes

Added a conditional fork to import necessary package using importlib rather than imp for Python versions >= 3.12. Code was written in a way to as not to introduce syntax that would not be understood by earlier Python versions (e.g. installed manually or from AUR).

Testing

Manually tested on ArchLinux with default Python installation.

References

• Answer by Levan Lovidze at StackOverflow

• importlib docs

[pokulo]

If dev = True is set to enable developement mode, import pacgraph from local folder should work. This MR moves all the importing of pacgraph into the if not dev: branch. Which renders the development mode broken (with no import).

Instead of hard coding the dev mode, we could first try to import pacgraph locally and catch the ImportError and only then attempt to do the import magic.