Updating .NET bindings to use webdriver.json for default Firefox profile.

Other language bindings have been using a common JSON file containing the
default profile setting for the anonymous Firefox profile used by the
Firefox driver. The .NET bindings now do the same.
Providing option to hide command prompt window for driver service executables in .NET bindings
Allow user to specify name of driver service executable in .NET

We now give an overload to CreateDefaultService for ChromeDriverService,
PhantomJSDriverService, and InternetExplorerDriverService to allow the
user to specify the name of the service exectuable. This is particularly
useful for non-Windows platforms where the executable does not end with
'.exe'. It also allows the user to rename the executable to a name of
their choosing and still be able to use it from the .NET bindings.