Msys build

Context

This merge request brings a new build on Windows using MSYS2.

Major changes

• MSYS2 build is now supported for Windows platforms

Minor changes

• Apache 2.0 license has been added to each file (more or less)
• [Flow] Transpiration boundary condition and dummy coupler have been added to prepare Amaury's work on viscous/inviscid coupling

Tests

• Passed on ubuntu 18.04, debian (gaston)