Paths of the rtt_roscomm_pkg_template folder differs in devel-space and install-space

Install-space deployments of package rtt_roscomm are currently broken as `${rtt_roscomm_DIR}` resolves to share/rtt_roscomm/cmake in `GenerateRTTROSCommPackage.cmake`. The template files should not be installed to the subfolder cmake in order to keep the path consistent between package source, devel-space and install-space.