wcps: supports domain() in coverage subsetting

[Bang Pham Huu]

WCPS should supports domain() for these cases:

• By default domain() returns an interval, it needs to support to get lo/hi on the result, e.g:

domain(c, Lat) return (20:40)
domain(c, Lat).lo returns 20
domain(c, Lat).hi returns 40

• domain() can be used for coverage subsetting, e.g:

  c[Lat(domain(c, Lat))] is equivalent to
  c[Lat(40:60)]
  

• domain() needs 3 parameter (coverage, axisLabel and axisCRS). But axisCRS can be omitted, e.g:

c[Lat(domain(c, Lat, "http://opengis.net/def/crs/EPSG/0/4326"))]

is equivalent to

c[Lat(domain(c, Lat))]