clinker & clustermap.js: automatic generation of gene cluster comparison figures

• Added -gf/--gene_functions argument for grouping genes by shared function/category, instead of just sequence similarity.

Given a 2-column CSV resembling:

Two groups are generated, Cytochrome P450 (GENE_001 and 002), and Methyltransferase (GENE_003, GENE_004).

• Updated clustermap.js. Gene groups now have tooltips when the corresponding label in the legend is clicked, and can now be easily merged to combine groups that share some function/category that did not group together by similarity alone