Add STATION_URL_TEMPLATE and Weather::extract_station_id()
More strictr matching for aviation weather's station ID
Add match for weather.noaa.gov URL
Add match for bare station id
Update weather URL when configured

- Configuration form now shows 4-letter station ID
- Plugin now accepts old URL, e.g.
  http://weather.noaa.gov/weather/current/RJTI.html
	new URL, e.g.
	http://www.aviationweather.gov/adds/metars/?station_ids=RJTI&std_trans=translated&chk_metars=on&hoursStr=most+recent+only
	and 4-letter station ID