Some distros do not contain the GrVersion.cmake module so the git
version can be applied into the gr-satnogs version reporting script.
This commits adds this module into the project, so the build system can
use it during project configuration.
The CMake build system will first try to locate libfec in the system. if
it is not available, it will start building the libfec that is part of
the gr-satnogs source code. During the installation libfec is installed
in the system, thus future builds will make use of it and will not
rebuild from source.