Detecting version number of VSIX

Detection of version number of VSIX by using VS ExtensionManager API by passing ProductID as argument. This was implemented as it was mentioned in the TODO
This should have the version number: `Include="Microsoft.VisualStudio.ExtensionManager, Version=12.0.0.0"`.

This is important if you have multiple versions of VS installed, it will always get the edge version. Like I currently have VS2013 and VS2014CTP3 installed..