Merge branch 'LHCBGAUSS-838.AmpGen' into 'Sim09-Upgrade'
LHCBGAUSS-838: New Amplitude model for D -> pi pi pi
New Amplitude model from @tevans. Changes in requirements and cmake build added (made with @clemenci).
Details at LHCBGAUSS-838
See merge request !26 (merged)