editor.js: show datasets created on successful query
Merge branch 'master' into dhalperi-show-datasets-created
datasets: remove download link for big datasets

Can only download datasets where we know the size and fewer than 100M cells.
(Number of cells is # cols * # rows.)
update test_myria_up to test both large and small datasets

- add TwitterK
- add numTuples for both Twitter and TwitterK
- check that Twitter's download link does not show in the page (too big)
- check that TwitterK's download link does show in the page (small)