LTR repeat glyph example

[cmdcolin]

You can get some of the way towards this by using just the existing glyph rendering system e.g. just manipulating color1, but there are weaknesses

1. There is a "repeat_region" element that is full length of feature
2. There is a "Copia_ltr_retrotransposon" (for example) that is a child of repeat_region, that is ALSO the full length of feature
3. Then there are other elements, that are also child of repeat_region

By making a specialized repeat glyph, we can render it a bit better, particularly the fact of of (2) not needing to be e.g. a transparent feature

This is a demo quality PR, but could be improved potentially

[cmdcolin]

Example screenshot