Warn if dropping potentially useful rows

[maurolepore]

In the interest of building a conservative, minimum viable product, we currently drop potentially useful rows. This is because we still lack some features planned for later. But this is not obvious and alpha users (e.g. Maxime) may be surprised to get meaningless biomass results.

The code should warn when dropping potentially useful rows. That should immediately add value by providing useful feedback to alpha users. And in the long run it also adds value because later we can write a unit test to check that this warning is now thrown once the code includes the features that we still lack.

[maurolepore]

• allo_find() should warn when dropping non-matching rows.

[maurolepore]

Still not finished with this. Until we implement generic equtions, allo_find() should warn if dropping rows not matching available species-specific equations.

[maurolepore]

allo_find() and allo_evaluate() are now more conservative. They no longer drop rows. Even if some rows can't be used to calculate biomass (e.g. because crucial values are missing) the rows stay in the data. This makes the process more transparent, and makes it easier to identidy what the problem might be.