improvement: render base numbers above chromatogram or below sequence

[rh-anocca]

Issue

When rendering a chromatogram the base-pair numbering is overlapping with the chromatogram.
It makes reading the numbering a poor experience and also clutters the chromatogram

Proposal

• When a chromatogram is rendered the numbering is moved above the chromatogram
• Alternatively, raise the "base" of the chromatogram, and place the numbering between the bottom of the chromatogram but above the sequence.