Coloring of genetic elements

[tolot27]

1371118 implements some static coloring of genes.

Automatic coloring of tRNAs and rRNAs like it is implemented in Mauve would be great, too.

Also coloring of transposases/insertion sequence elements would be realy good because they are often involved in rearrangements. Unfortunately, they are not annotated with feature type mobile_element, mostly. Hence, parsing the product for "transposase" is necessary.