Improve the menu 'Kind'

[lpatiny]

Once we can name the molecules:

• Add the possibility to 'label' the molecule #1342

We could improve the menu that allows to select the Kind

Still something to think about because 'Signal', 'P1', 'P2', 'P3' should be probably replaced by the molecule.label (and probably store using as value molecule.id so that label could be changed).

Once this is done we will be able to calculate the relative integral per product.