Coloring by multiple variables

[ondovb]

Parametric coloring in the chart could be selected by a dropdown instead of a checkbox. The XML format would have to be modified to allow multiple <color> tags. Import scripts could utilize this with built in variables (e.g. both e-value and score for BLAST results) or generic columns in text import. The Excel template would be tricker and may need to move to a flexible column model. Suggested in #44.