Almost final version of scanning tools.

Almost final version of scanning tools.

* AliEveEventManager
  Emit new signal NewEventDataLoaded() after the event-data is
  connected but before the macros are executed.

* AliEveTrackCounter
  Connect to AliEveEventManager::NewEventDataLoaded() to do the reset.
  Introduce 'Bool_t fAcitve' -- now that track and tracklet label is
  misused to store scanning results it is better that track-counting
  is not enabled by default.

* AliEveTrackCounterEditor
  Add Activate / Deactivate buttons and handlers.
  Remove histogram plotting code -- now in show_scan_results.C

* visscan_init.C
  Remove code for registration of tracks/tracklets to
  track-counter. This is now done in esd_tracks / esd_spd_tracklets.

* make_scan_results.C
  Create the scan-result tree from individual objects stored during
  scanning.

* show_scan_results.C
  Create canvases and plot basic stuff from the scan-result tree.

* esd_spd_tracklets.C
  Put tracklets into two containers -- Good/Bad.
  Register the tracklets to track-counter if it is active.

* esd_tracks.C
  In esd_tracks_by_category() register the containers to track-counter
  if it is active.