Added support for getting app sessions by User [ListCurrentAppSessions()...

I tried compiling the solution, but could only do so after adding a reference to TerminalVelocity manually - don't know how to fix the nuget package.  Our R# automatically adds a copyright date, which can be ignored.

I think this is useful (I have tried the API and it seems to work fine)
Is it possible to remove this copyright?  I wouldn't feel comfortable merging this in unless it was free from these types of legal markers.