Allow using the library without API access

[pR0Ps]

This library should have it's scraping functionality refactored into a separate class (ScrapingClient?) that can be used without touching the API. The WebClient class can simply instantiate and use that class to extend stravalib's Client class.

This enables the scraping client class to not only extend the API, but to provide scraping-based replacements for other API methods (ie. listing activities, getting activity data, etc). This gives users of the library the choice of using a stravalib-compatible class, or relying completely on scraping and not having to set up an API application at all (a huge pain).