A few updates to java-client

Hi,

I've forgot to merge several commits from my local repo w/ the following changes :
- added MobilePlatform interface (Android, IOS, FirefoxOS)
- added MobileBrowserType interface (Safari, Browser, Chromium, Chrome)
- added MobileCapabilityType.APP_WAIT_ACTIVITY
- fixed small Integer cast issue (in Eclipse it won't compile)
- set -source and -target of the Java Compiler to 1.7 (for maven compiler plugin)