New Screen1 option: set AppName

In the current implementation, the default app name is the project name. In the current internationalization framework, we can't name the project to something other than English. This is not friendly for the people who want to name the app to something non-English. 

I added a new property, Screen1.AppName and default to "" (empty string). This property will be saved in the project.properties file within the youngandroidproject folder in the aia file. 

The app name is default to project name. But when Screen1.AppName is set, the display name of the installed app will use Screen1.AppName. I checked on the Android document, there is no restriction on the app name as long as it is a string (android:label). 

I have tested this with the following case - I uploaded an old project which doesn't have AppName property and the project loaded fine. If the AppName property is triggered, the system would write the values to the project property file. 

@halatmit @jisqyv @afmckinney @josmas @kkashi01 @app-inventor-dev@googlegroups.com