replaced sync methods with corresponding async versions

I am Semih Okur, a PhD student in the CS department at the University of Illinois. I'm currently doing research on asynchronous programming in phone applications. I found many misuses of async/await keywords in Windows Phone applications. One typical misuse is that developers use synchronous method calls in async methods. However, these synchronous method calls have corresponding asynchronous versions in .NET API. I executed my automated static analysis tool to detect these cases and found some opportunities about asynchronous programming in this application. 

Please review my pull request