Added a reload function.
Stopped destroying the webview on every launch.

If we're relaunching the same app, we reload the webview.  This handles the most annoying `cca push --watch` case.
If a new app is being launched, though, the webview is still destroyed and recreated (for now).
Updated webview reload to take arguments.

It now takes and obeys the same arguments as `create` does...
...except Android doesn't switch webview types yet.
Removed unnecessary checks.

By default, on Android, if a "system" webview type is specified, then we use the system webview; anything else and we use Crosswalk.