* The TabletScriptingInterface destructor is invoked on app shutdown after the logging system has been destroyed.
To avoid this I removed the destructor. The log was only for debug purposes anyway.
* Removed calls to setProperty() these calls are not thread safe and were causing asserts during debug.
Instead of getting and setting the property we maintain the TabletProxy state using an enum.
Help button has been updated to switch to the help.html. It doesn't look good because
the content was authored expecting landscape window, not portrait.
The API is by no means final. But it exposes two methods to JS.
* Tablet.gotoHomeScreen() - Used to forcefully go back to the home tablet "springboard", eventually this will
hooked up to the tablet button.
* Tablet.gotoWebScreen(url) - Causes the tablet to switch from the home "springboard" and load a web url.
tabletTest.js and help.js have been updated to use this functionality.
