Add exon number

Given a track with mRNA annotations, a new track will be created in which variants are annotated with the numbering of the corresponding exon with numbered exons based on the transcript annotations in the input track (see an example of a result in figure 23.2).

Image exon_number_result
Figure 23.2: A variant found in the second exon out of three in total.

When there are multiple isoforms, a comma-separated list of the exon numbers is given.