Rework coupling model#6

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jgiret wants to merge 3 commits intooptimad:reworkCouplingModelfrom

jgiret:reworkCouplingModel

Commits on Oct 5, 2020

Create test for GEMS toy problem
Jean-Christophe Giret
committed

Commits on Nov 30, 2020

Add test for disciplines, chain and MDA
Jean-Christophe Giret
committed
Modification on coupling cpp and hpp files
Jean-Christophe Giret
committed