On making tests fails with:

../bin/testrunner: error while loading shared libraries: libomp.so:
    cannot open shared object file: No such file or directory

Add error message when trying to build Gui with CMake 3.9.x.

Various fixes from #1907

[web] Fix binary files not commited with git-lfs

Related:
- #1887
- https://stackoverflow.com/a/340683/80480

This slipped through as currently macOS is not tested via CI.

This reduces download times significantly as downloaded decreases
from over 1 GB to around 60 MB.

Closes #1906

in future CMake version. Fixes a warning on CMake 3.9.

Use png for images. Fix sections in the markdown.

Vector extrapolation part2

Restructure ThermoMechanics

Writing the code inplace saves few lines and makes
it more comparable to the SmallDeformationFEM.

This allows not to include the TMFEM.h in the process implementation.