Datatype specific operators

[jonathan-wcc]

Currently GXP (querybuilder) allows all operators to be used with all datatypes. It should probably only show the operators that are allowed on that type of data.

I think the OpenGIS Filter Encoding 2.0 Encoding Standard says what should/shouldn't work: http://www.opengeospatial.org/standards/filter - but there may be other standards.

i.e.:
"The PropertyIsLike element is intended to encode a character string comparison operator with pattern matching." - so I guess that means LIKE should probably only be available for string datatypes.

[ahocevar]

Agreed. Pull requests welcome.