Always use CDN as JS servers

[berinhard]

This PR implements some required tooling in order to make #186 PR possible for being fixed and it also changes the default behavior of pyp5js when it comes to static files.

Currently, pyp5js copies a p5.min.js file to the every new sketch's static dir. This wasn't a problem until Pyodide, which has more the 10MB of JS related files. To copy 10MB per sketch would be abusive with our users HDs and thus, from the very beginning, pyp5js used CDN as our pyodide serve. The #186 was created as an alternative to that for the web editor.

During the process I realized that:

1. CDN should be the default for all the Javascript dependencies;
2. The user should be able to opt-out CDN usage (pyp5js new --local) too;
3. The web editor must always use local JS so, that way, people can use pyp5js even without internet access;

This PR implements all the changes on this directions and leave TODO notes to map what should be done when it comes to pyodide local copies.