Improvement: extract interface

[samba2]

Extracted the FileSystemWatcherEx API into separate interface IFileSystemWatcherEx. Mainly to simplify testing via e.g. Moq or own alternative implementations.

To clarify: should the documentation also remain in FileSystemWatcherEx (duplication) or should we just have it in the interface and hance delete the comments from FileSystemWatcherEx ?

[samba2]

additional remark: this was an automated refactoring.

[samba2]

just some additional thoughts:

• maybe we should make the interface slimer. Really just focus on behavior
• we probably should also use the interface in the demo app and in the unit tests, so somthing like IFileSystemWatcherEx fw = new FileSystemWatcherEx(...)

[d2phap]

Thanks @samba2 !