Error messages for single assemblage or wrong assemblage

[stheroux]

The package should return an error message if:

1. User has SBA names in an “integrated” fraction
2. User has diatom names in “microalgae” or “macroalgae” or “qualitative” fractions
3. The ASCI output should only return D_ASCI if only “integrated” fraction is submitted (no H_ASCI calculated). Also, only S_ASCI calculated if only “microalgae” and/or ”macroalgae” fractions are submitted. H_ASCI only returned if BOTH “integrated” + micro/macroalgae fractions are submitted.