Better downloads

[ivirshup]

Description of feature

Currently we grab data from bioconductor's AnnotationHub. This is very convenient, but we're grabbing uncompressed sqlite files. When bioc distributes these files as packages, they are gzipped. It turns out this data is very compressible and can be shrunk considerably.

I've had previous discussion with the bioc team if they could provide compressed versions of these files on annotation hub. This issue is tracking that.

[thomas-reimonn]

My previous comment about opening a database over https wrong. Never mind.