cmake build system: unify fft detection code

Signed-off-by: Tim Blechmann <tim@klingt.org>
external libraries: move nova-tt to github & unify implementation

Signed-off-by: Tim Blechmann <tim@klingt.org>
common/lang: mutex transition - correctly define BOOST_CHRONO_HEADER_ONLY

Signed-off-by: Tim Blechmann <tim@klingt.org>