Metadata - extent - improve controls

[mborne]

Document and implement the following checks :

-180,0 <= West Bounding Longitude Value <= 180,0
-180,0 <= East Bounding Longitude Value <= 180,0
-90,0 <= South Bounding Latitude Value <= 90,0; South Bounding Latitude Value <= North bounding Latitude Value
-90,0 <= North Bounding Latitude Value <= 90,0; North Bounding Latitude Value >= South Bounding Latitude Value