Reverting a fix to include Microsoft.AspNet.FileSystems.Interfaces as a build time dependency

MVC & Hosting has dependency on both implementation from Microsoft.AspNet.FileSystems & interfaces from Microsoft.AspNet.FileSystems.Interfaces. Since Microsoft.AspNet.FileSystems.Interfaces was made a build time dependency, MVC repo broke. Reverting the change.
Reacting to System.Threading version changes
Updating tests to use official xunit
Handling the directory rename case for file system watcher

Today when a trigger is registered for items under a directory and when the directory is renamed FSW only fires an event for the directory change, but not for the files/sub-directories under it. So if there are triggeres setup for sub-items, they they trigger on folder rename. This fix addresses the issue, by handling a directory change event and raising the trigger for the file system entries under the renamed directory.