Single file deliveries

[farski]

Currently all extract jobs are being run with a * wildcard name, meaning BigQuery can create multiple files at its own discretion. For large queries or partitioned tables, this will pretty much always result in multiple files, even if not strictly necessary based on file size limits.

Two possibilities to consider:

1. An option or default to try one file first, and fail over to wildcard if BigQuery indicates the export was over the limit.
2. Add the ability for us to concatenate down to a single file before delivery to the final destination.