chenlei92324336

build-in post-processing 2D plots with Gnuplot, new examples powerLaw2d (non-Newtonian fluid) and tgv3d (turbulence model benchmark), revised VTK data

simplified user friendly converter, new thermal examples and poiseuille3d example, gnuplot based plotting functionality, WALE based turbulence model,

build-in preprocessing with image files, parallel backup of simulation states, support of non-Newtonian fluids, support of particle suspensions: Euler