(ngx-features-viewer) Bind data to traces and features

[damiclem]

Traces and features are representations ove a sequence of some kind of annotation. Data underlying annotations must be bound to traces and features. This would allow to express useful information in labels and traces.

To bind data to features, we add the data property to the feature interface. This would require the tooltip to access such data, in order to be fully customizable.

For example, la locus mapped from PDB to UniProt sequence through SIFTS might need to express its start, end boundaries in term of PDB indices: 1A-99B instead of 1-100.