Changes to the starting view, max extent, within-area warnings, etc and adding scale-dependency to markers

- Yesterday, warnings were removed when your location is outside the area. So MAX_EXTENT is no longer used, and has been removed entirely.

- Replaced START_W START_S START_E START_N with simply START_LAT START_LON START_ZOOM so the starting view is more consistent over varying screen sizes

- Removed MIN_ZOOM and MAX_ZOOM in favor of START_ZOOM-2 and START_ZOOM+5

- Added minZoom and maxZoom to MAP constructor

- Added scale-dependent visibility to markers in OVERLAYS['ostpoints'] and mediapoints and closurepoints. Changed were to selectSeason_RenderMapContent() to fire zoomend event, to initMap() to add the zoomend handler, to L.Marker prototype to add show() and hide() methods, and to OSTPOI_TYPES to define their minZoomLevel
Season change: in init() the check for which season should be used based on current date, was using wrong variable name