Fix multiple bugs
Fix multiple bugs

- Logs are grouped by path so that bookmark repository for each group is
  throttled by appropriate settings. Previously no grouping so updates could
  be missed.
- Notify correctly on deleting of files
- Protect multithreaded access to the file changes observer. Use lock to sync
  changes picked up from poller and those from FileSystemWatcher
- Reset stream position to beginning of file if file size is now less than
  current position (happens if file is truncated)

emertechie/CsvLogTailer,emertechie/CsvLogTailer