Add support for PostGIS raster

[tfr42]

deegree shall support Raster TileStore for PostGIS raster.
See http://postgis.net/docs/RT_reference.html

[tfr42]

We are seeking community feedback if users would like make use of PostGIS Raster as a source for raster data.

This new feature may relate to the activities documented in issue #977 which shall result in a better performing deegree WMS.