Update flow and windows libs

Context

This MR brings some improvements to waves, mainly to the flow module.

Changes

• [general] Minor fixes
• [general] Added configuration for windows libs (visual studio 2017 + python 3) by @L.Papeleux
• [tbox] Jacobian matrix and inverse are now computed using fixed-size matrices
  • Fixes issue #27 and decreases runtime (slightly)
• [tbox] Cleaned element matrix computation for mechanical, thermal and thermo-mechanical computations
  • build...() methods in Element are now easier to read, like the other methods
• [flow] Added sideslip angle input and sideforce computation
• [flow] Added class F1ElVi to handle freestream velocity
  • B.C. are now enforced only using angles of attack and sideslip
• [flow] Added minimum limit to Cp computation
  • loads are always valid. This is useful for coupled computations (CUPyDO) where intermediate solutions might be unphysical
• [flow] Added more default initializers
  • Reduces the number of c/c lines in tests/
• [flow] Added case Coyote
  • Full aircraft with sideslip
• [flow] Force gmsh to use Delaunay mesher in 2D (thanks @L.Papeleux)
• [mirrors] git-lfs is now used for the mesh (.apdl) and result (.ansys) files

Tests

Passed on ubuntu18.04 (python 2.7.15), ubuntu20.04 (python 3.8.2), debian9.12 (python 2.7.13), msys2 (python 3.8.1).