Null identified larvae cannot be selected
Problem: Moving objects with id 0 cannot be selected from the assay plot.
MWT has 1-indexed moving objects and, to avoid union types that can accommodate undefined values (Nothing), LarvaTagger.jl encodes undefined larvae with a null id.
FIMTrack has 0-indexed moving objects and the introduction of support for FIMTrack files revealed the issue.
Proposal: Either admit a union type or pick a different unrealistic value to represent undefined larva id.
This issue was last-minute fixed in commit ec8bca02 prior to v0.3 release.