Fix maxResults behavior and extend client read volume logging
Properly set the content type in the response
Add a .gitignore file to list files that likely shouldn't be included in the repo (like google_api_key.txt).
Read search optimization: don't request reads in the range we already have.

This substantially reduces transfer volume (and update latency) in some cases,
like panning along at full read-view scale.

Also remove trailing whitespace I accidentally added.
Fix EBI backend support by emulating partial response support for reads

NCBI and Google support partial responses (https://developers.google.com/genomics/performance#partial-response),
but EBI does not.  Things are simpler and more performant if the client
can assume this support exists.  So emulate it for EBI in python.