Handle no elementId

[stoneman]

The elementId parameter is not specified in the Set Orientation definition:

http://appium.io/docs/en/commands/session/orientation/set-orientation/

Since the SetOrientation handler in espresso server requires an elementId parameter, the java-client's device.rotate(ScreeOrientation.LANDSCAPE) method produces errors like this...

org.openqa.selenium.WebDriverException: An unknown server-side error occurred while processing the command. Original error: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Object.hashCode()' on a null object reference
                at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:915)
                at java.util.concurrent.ConcurrentHashMap.containsKey(ConcurrentHashMap.java:943)
                at io.appium.espressoserver.lib.model.Element.exists(Element.java:100)
                at io.appium.espressoserver.lib.model.Element.getViewInteractionById(Element.java:78)
                at io.appium.espressoserver.lib.handlers.SetOrientation.handle(SetOrientation.java:35)
                at io.appium.espressoserver.lib.handlers.SetOrientation.handle(SetOrientation.java:30)
                at io.appium.espressoserver.lib.http.Router.route(Router.java:277)
                at io.appium.espressoserver.lib.http.Server.serve(Server.java:65)
                at fi.iki.elonen.NanoHTTPD.serve(NanoHTTPD.java:2244)
                at fi.iki.elonen.NanoHTTPD$HTTPSession.execute(NanoHTTPD.java:945)
                at fi.iki.elonen.NanoHTTPD$ClientHandler.run(NanoHTTPD.java:192)
                at java.lang.Thread.run(Thread.java:761)

This PR modifies the SetOrientation handler to use onView(isRoot()) when elementId is not provided. Support for the elementId parameter should possible be removed entirely?

[jsf-clabot]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

[stoneman]

Closing as I can't sign that CLA