#16 projection is used for creating Basemap
lon_0 and lat_0 are fetched from proj4string into Basemap
#16 self.lon/lat and self.x/y are not created when Nansatmap is initiated
#16 self.lon/lat and self.x/y are created on deman in self.create_xy_grids and create_lonlat_grids only when needed
#16 create self.lon/lat and self.x/y on deman
Merge branch 'nansatmap-fix-projection' into develop
Merge branch 'develop' of https://github.com/nansencenter/nansat into develop