New release of core lib and fracture module

[Lukasz Kaczmraczyk]

New release mofem core (v0.8.18) and fracture module (v0.9.50)

Core lib v0.8.18:

1. Improved robustness of mesh cutting when passing through corners.

2. Improved med file reader

Fracture module v0.9.50:

1. Improved convergence, efficiency and robustness for internal stresses.

To install with spack:

git clone --single-branch -b mofem https://github.com/likask/spack.git

spack install mofem-frac...@0.9.50

spack view symlink -i fm_view_v0.9.50 mofem-frac...@0.9.50

Kind regards

Lukasz