Properly install CMake files

Foreach is not necessary, they can be intalled all at the same time
Add variable YARP_MODULE_DIR and use it where necessary

Also use CMAKE_CURRENT_LIST_DIR where it can be used
[Cleanup]
It's not necessary to expand variable
Use list instead of set to append YARP_MODULE_PATH to CMAKE_MODULE_PATH
remove un-needed policy CMP0017 OLD; insertion of additional yarp_module_path is now conditioned by CREATE_GUIS