Report number of stations that are in windfield extent

[wcarthur]

When running tcevent.py and collecting timeseries data, the station list is loaded before the extent of the wind field is determined. On loading, code reports number of stations that will collect time series data, which is always the total number of stations contained in the file.

22:42:19: Loading wind field calculation settings
22:42:19: Loading timeseries stations from /opt/tcrm-processor/tcrm/input/stationlist.shp
22:42:20: There are 13868 stations that will collect timeseries data
22:42:20: Running windfield generator
22:42:20: Dumping gusts to /opt/tcrm-processor/tmp/output/windfield
22:42:20: Processing 1 track files in /opt/tcrm-processor/tmp/output/tracks
22:42:20: Calculating wind fields for tracks in /opt/tcrm-processor/tmp/output/tracks/tracks.interp.nc
22:42:20: No grid limit set - returning all tracks
22:42:20: Wind field domain set to {'xMin': 152.0, 'xMax': 160.0, 'yMin': -29.0, 'yMax': -14.0}

Update to report number of stations that lie within the wind field extent.