[code] Refactoring : split the core code, config, the logging and the UI

[artesim-zz]

The maintenance, testing, and future developments will be easier if we take some time to refactor the code a bit.

I think we should split the code roughly in these separate modules :

• the core code, where most of the functionality lies.
• the management of the config file(s) and options (see this idea)
• the logging (in file + console log in the UI) => I know the standard python logging module, seems ideal for that.
• the UI (once separated from the rest, we could imagine switching to Qt for instance).

Also, this would help with the test suite efforts initiated by @girotobial in this issue.

Although one of the use cases for a test suite is ensuring that refactoring doesn't brake anything, but still...