New models, two triplet, 3 diffusion times

[paulmueller]

• [x] T+3D+3D+3D
• [x] T+T+3D+3D
• [x] T+T+2D-3D
• [x] all confocal models without triplet
• related to #59 and #40

If it is possible to use submenus in the model selection dialog upon file import, implement all possible combinations of T, TT, 3D, 2D.