Refactor relative imports

Addresses a need for the following: changing instances of imports which are relative in nature to become absolute.

Justification: I propose that absolute imports would provide the following aspects to our codebase:

Clarity: Absolute imports provide a clear indication of where the imported modules come from. When you use an absolute import, you explicitly specify the complete path to the module or package that you want to import, which makes it easier for other developers (and your future self) to understand the structure of your project.

Avoiding naming conflicts: When you use a relative import, you risk running into naming conflicts if multiple modules with the same name exist in different packages. With an absolute import, you can ensure that you're importing the correct module every time. This is particularly pertinent in this repository's case.

Future-proofing: Absolute imports are more future-proof than relative imports because they're less likely to break if you refactor your code or move modules around in your project. If you use relative imports and then move a module to a different location in your project, you'll need to update all the relative import statements that reference that module.

Consistency: Using absolute imports throughout your project ensures consistency in your codebase, which can make it easier to read and maintain.

biosimulators / Biosimulators_COPASI

Refactor relative imports #63