Add Latch class to nfCommon

[lookeypl]

Right now ThreadPool uses Latch as a synchronization point in tests. This class might be useful in other places.

• [x] Create new Latch class based on the one used in ThreadPool tests
• [x] Add tests if possible
• [ ] Use WinAPI/pthread instead of STL
• [ ] Allow for various types of synchronization:
  • [x] Waiting for single event
  • [x] Waiting until timeout occurs
  • [ ] Active waiting for event (probably will be rarely used, but sometimes in debugging might be helpful)
  • [ ] Waiting for N events
  • [ ] Combinations of mentioned above waiting types

[mkulagowski]

Windows part of this task may easily be done with events in WinAPI (CreateEvent(), SetEvent(), ResetEvent() and WaitForSingleObjectEx())