Properly retrieve meta when there are no rows

Change-Id: Ifaf1c5a90eed1a4de3fc07405125727c57d4fe8a
tx/__init__.py: Use vi[0]

Change-Id: I4e96b41a8e548448449ef1622afe08c7f07b126f
Make http result callbacks rate limited

Change-Id: I1f6c735e042eec98ef9dd1584a1f140a1803376d
Only extract http meta if data is dict

Change-Id: I524fe6bde6d7e89f2e34124a466cb469a4539202
Async/Tx view interface

Change-Id: Ied7aaca4aa6c2adb0f931f698ad034031ade7e8c