Experimental revamping of dependencies build system

* Switch back to using cmake's option command for configuring nomlib's
top-level build units.

* Introduce experimental BuildTreeDeps.cmake script; the script simply
ensures that the options chosen have their applicable dependencies
added, without the end-user needing to be aware of the details.

* config.hpp.in: Introduce experimental NOM_USE_SDL2_IMAGE,
NOM_USE_SDL2_TTF, NOM_USE_OPENAL and NOM_USE_LIBSNDFILE
cmake build-time config vars; these are used in examples/device_info.cpp
as an experimental test for the time being.

* Revamp examples/device_info.cpp: Use SDL2Logging facilities for
output and add dumping of library versions for nomlib, SDL2, SD2_image,
SDL2_ttf, OpenAL and libsndfile.