have all or nothing create for API client

[sdtaylor]

Ran into an issue where forecasting entries from the static image metadata file were duplicated, causing the API update to error out from duplicate entries, causing an imcomplete API update and website errors. Not sure where the duplicates came from, but a good guard regardless is having an all or nothing update for every forecast iteration inside api_client.py. There is likely something for this built into the django stuff.