Color code sequences with issues

[djlohman]

This might be challenging to implement, and I would view this not essential to developing version 2.0. Nonetheless, it would be extremely useful.

Color code cells in the main window: pale yellow if there is codon info, pale orange if there are N’s, and pale red if there are gaps. If more than one of these states is true for a single cell, then the more dire state should be color coded: from codon info to Ns to gaps, as most dire.