Ensure API fills out pagination metadata (nextPage, prevPage, count)

[osterbit]

(moved to separate issue, originally from #84 ) "[make sure] our api properly fills out pagination metadata: nextPage, prevPage, and a new count property that shows list length"

[b5]

I think we should throw a little more time into making sure this works. It'll help us make inroads on the body pagination / loading issues we're having on the frontend:

We need to build in the ability to preview the first 100 rows of a dataset found on the qri web page. This would be in addition to the standard data we display (metadata, title, etc). The "discoverer" would still need to download qri in order to access / see / download the full dataset. The intention of this is only to show the "discoverer" some basic info on the datasets stored on the d.web