js/my_queries.js: use the API call to only fetch my queries

from /REST.svc/v2/db/dataset
to   /REST.svc/v2/db/dataset/<my_username>

For dhalperi@washington.edu, this makes it go from ~1.6MB to ~75KB download.

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>