L8 L2A Bulk Download Support

This release works with the S2D2 API v0.3.0 to support batch downloading for L8, to bring it in line with the functionality for S2.

The USGS Earth Explorer has been having technical issues over the last month or so, resulting in work being done to restore L8 querying. The L8 querying and batch downloads should be working now, but this restored functionality hasn't been tested thoroughly.