Hardcode conf.yaml path

This was a problem I noticed in RStudio, where the cwd would affect finding of
conf.yaml. Thus, hardcoding that fixes our issue.
Cache datasets by checking if file exists
Merge remote-tracking branch 'origin/get_cache'
Use objects interface to bioblend.

Its a higher-level, more correct interface. Especially for downloading - it actually correctly downloads against the API unlike the other end-points which target the web controllers and require the datasets to be public.