Support chip command

[lewfish]

The goal is to implement the methods in the backend (and any stuff needed in the config and configbuilder) that allow the chip command to generate training chips in the gluoncv format to be consumed by the training routine. Time estimate: 1 week

prep tasks:

• install gluoncv
• download data
• study keras_classification backend and config

tips:

• get it to work locally first (might want to make a PR for this, and a second PR that adds and tests functionality for running remotely)
• try to use "directory for each class" dataset format if possible. you'll need to think about how the train method will work to see if this is possible.