Small CMake modification to MacPorts and Homebrew detection to fix OCE

This MR fixes Homebrew and MacPorts detection in OCE by unsetting appropriate variables if the installation has not been found. Consequently, OCE detection now works properly for Homebrew.

See merge request !729

fix/surface-mesher

Fix bug in compilation, tests and surface mesher.

See merge request !728

meshing update for madrid

This updates a number of the 2D meshing routines to be more useful for the tutorial in madrid. I.e removing unhelpful IO
Also has some minor updates to the documentation.

See merge request !726

Fix/fc read dat

Fixes related to isocontour: Corrected the tolerance and restructred logic to globalcondense in ProcessIsoContour, Updated the InputDat.cpp file to be case insensitive.

See merge request !719

Add variational optimisation framework to NekMesh

This adds the variational mesh optimisation framework to NekMesh. Its now throughly tested for triangle, quad, tet and prism meshes along with triangle/quad and prism/tet hybrid meshes. Although not perfect we've got a pretty good grasp of how it behaves and why. Future work will be to move this code into a library as a "variational solver" where NekMesh utilises this along with alternative solvers.


See merge request !711

2D Mesh Generator

A 2D mesh generator including a NACA aerofoil generator.

Ready to merge.

See merge request !720