Incremental loading P2 Add update-dataset to bash

[alexglasertpx]

Overview
Following from ticket #352 we now want to add a new function to the bash scripts and check results are valid.

Checklist

• Create a command called 'dataset-update' in cli.py, that calls the already merged update_dataset command in commands.py [0.5]
• Create an 'update-dataset' make variable (that is similar to 'build-dataset' but calls the dataset_update function) [0.5]
• For each other command (in update-dataset) check that when we run with new resources that the outputs are the same as the old method [2]
  • Ensure that resource.csv has elements added to them rather than just printing out the new resources only
  • Pay close attention to csvstack
• Add acceptance test 'test_dataset_update' (should be quite similar to 'test_dataset_create') [1]