Allow CommandProvider to "re-initialize" fresh web driver

[ffMathy]

Currently if I decide to use FluentAutomation and I want to switch driver at runtime or I want to kill and re-open the driver because it has been exhausted due to memory issues, I can't, since the CommandProvider has cached the old IWebDriver instance.

This solution proposal adds a new protected method that allows me to clear that cache and force a re-initialization.

Please let me know what you think.