Commands other than `open` are slowed down by GUI dependencies

Among the commands for the larvatagger.sh and larvatagger.jl scripts, only open requires the GUI dependencies. The other commands, including import, train, predict, do not need packages such as Makie.

Problem: Makie takes a while to load (and also to reload).

Proposal: Find a way to conditionally load JSServe and Makie/WGLMakie.