Add autoWebview capability

Milestone 1.2 issue #2715

Allow user to enter directly into webview context. Adds universal capability `autoWebview` (`true`/`false`) and Android capability `autoWebviewTimeout` (in seconds, defaults to `2`), to set hot long to wait before checking for the webview. 

Also fixes Android/Selendroid webview tests.
doesn't ./reset.sh --dev take care of this? If so, no need for the notice here, since tests require ./reset.sh --dev to have been run. If it doesn't take care of this, we should make it do so.