Make models errors

[lizgzil]

When we download the models we look for all the artefact_targets, but these are out of date to the format the multitask models are saved in so we get the error:

(base) 01763-IA-GallaghE:deep_reference_parser gallaghe$ make models
aws s3 cp s3://datalabs-public/deep_reference_parser/models/multitask/2020.4.5_multitask/char2ind.pickle models/multitask/2020.4.5_multitask/char2ind.pickle
fatal error: An error occurred (404) when calling the HeadObject operation: Key "deep_reference_parser/models/multitask/2020.4.5_multitask/char2ind.pickle" does not exist
make: *** [models/multitask/2020.4.5_multitask/char2ind.pickle] Error 1

So I think the artefact_targets need to be downloaded if they exist but skipped over otherwise.

Also I think indices.pickle needs to be added to the list of artefact_targets.