GDAL integration and dataaccess modules

Integrates the popular GDAL framework (http://www.gdal.org/) into deegree. It adds the following modules:

* deegree-core-gdal: Common functionality for accessing GDAL via JNI
* deegree-tilestore-gdal: Tile store implementation based on GDAL
* deegree-layers-gdal: Layer implementation based on GDAL

These extension allow to use all raster raster formats that are supported by GDAL to define WMS layers or tile stores in a deegree workspace.