Use Python-based Build Tools via pipx

[kilo52]

For Python-based projects all build tools which require Python are simply part of the project's requirements.txt file. But for non-Python-based projects, the default project control code generated by project-init requires our standard virtual environment + virtualenvwrapper utilities to be available if the tool is not available on the path (i.e. the command cannot be found). For build tools which require Python, the generated project control code should check with pipx if the tool can be installed and make it available.