Improve proj4j tests to reflect the recent changes and the moved out EPSG resources

[pomadchin]

After separating the project into two, we may get some confusing errors; i.e.

java.lang.IllegalStateException: Unable to access CRS file: proj4/nad/epsg
  at org.locationtech.proj4j.io.Proj4FileReader.readParametersFromFile(Proj4FileReader.java:44)
  at org.locationtech.proj4j.io.Proj4FileReader.getParameters(Proj4FileReader.java:119)
  at org.locationtech.proj4j.CRSFactory.createFromName(CRSFactory.java:83)
  at org.apache.calcite.runtime.ProjectionTransformer.<init>(ProjectionTransformer.java:57)
  at org.apache.calcite.runtime.SpatialTypeFunctions.ST_Transform(SpatialTypeFunctions.java:[1196]

This task is to improve error messages and documentation.

cc @bchapuis