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).

CMake/gaston-clang-Py3.cmake

+# Copyright 2020 University of Liège
+# 
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+# 
+#     http://www.apache.org/licenses/LICENSE-2.0
+# 
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+FIND_PROGRAM(CMAKE_CXX_COMPILER NAMES clang++)
+FIND_PROGRAM(CMAKE_C_COMPILER   NAMES clang)
+# enable Py3
+OPTION(USE_PY3 "Use Python3" ON)
+SET(VTK_DIR "/opt/vtk/lib/cmake/vtk-7.1" CACHE PATH "" FORCE)
+# Trilinos not compiling with clang (check to wiki to fix)
+LIST(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR})
+INCLUDE(disable-trilinos)
+