WindowsPhone: MPfm.Sound now builds correctly under Windows Phone. However, some critical code dedicated for this platform hasn't been implemented (or WindowsStore/PCL) and won't be before a while. The idea is to see what are the limitations of the platform for now.

Related to issue #424.
WindowsStore: Now building MPfm.Sound correctly. Once again, added a ton of preprocessor conditions with missing implementations for Windows Store. Most of the preprocessor conditions are related to System.IO (loading/saving metadata with custom classes such as SV7Metadata, SV8Metadata, APEMetadata, etc.). Also missing the BASS.NET wrapper because it is not available on WinRT.

Related to issue #423.