add euscollada_SOURCE_PREFIX and euscollada_PREFIX

I'm not understand well, but it seems 3 patterns when we'd like to access to the package path which we used to `rospack find` in rosbuild.
 <package>_SOURCE_DIR -> src directory with one workspace
<package>_SOURCE_PREFIX -> src directory but multiple workspace, that means jsk_model_tools installed in <opther workspace>/devel
 <package>_PREFIX or <package>_DIR/../ -> installed directory