Include more info in API requests for a CRS

[Kristian Evers]

The /crs/{crs}/ API entry should return the area of use, valid bounding box of the CRS, the units of the various coordinate values.

An example:

> curl https://services.kortforsyningen.dk/rest/webproj/v1.1/crs/EPSG:4096
{
  "country": "DK",
  "title": "ETRS89 / DKTM Zone 4",
  "title_short": "ETRS89/DKTM4",
  "v1": "Easting",
  "v1_short": "x",
  "v1_unit": "m",
  "v2": "Northing",
  "v2_short": "y",
  "v1_unit": "m",
  "v3": "ellipsoidehøjde",
  "v3_short": "h",
  "v1_unit": "m",
  "v4": null,
  "v4_short": null,
  "v1_unit": null,
  "area_of_use": "Denmark - onshore Bornholm",
  "bounding_box": [54.94,14.59,55.36,15.24]
}