Implemented a method to inject media to BS device which accepts BS media URL as parameter

[snehith07]

• Created an overloaded method injectMediaToDriver() in BrowserStackImageInjection.java, which injects media to BS device which accepts BS media URL as parameter
• Added a method to the Driver class injectMediaUrlToBrowserstackDevice(), which calls the above method.
• Added a method to the Driver class, isMobilePlatform(), which returns a boolean value after checking whether the current platform is mobile or not, to reduce the complexity of the above method.
• Made this method public, thus can be used across the framework.