bugfixes, store MUMPS source outside of build dir

store upstream source outside of build directory -- allows flipping between MUMPS versions without redownloading source each time, which can be quite slow due to server / internet bandwidth

remove MUMPS source code download timeout

remove GNU Octave to save maintenance burden

test: use TEST_LAUNCHER (better practice in CMake)

tests default on if top level project

bugfix: GEMMT: was broken several months ago, now fixed