when memento enabled, the timegate now follows memento pattern 2.2 (http://tools.ietf.org/html/rfc7089#section-4.2.2)
also return content-location instead of location, update memento no-redirect tests to match new behavior. closes#122
frames: add request_ts to wbinfo and use that as the timestamp in the top-frame. for exact replay, request_ts == timestamp
for latest replay / no timestamp / memento timegate, redirect to current time instead of time of last capture, while serving
last capture.
timeutils: add timestamp_now() function to return timestamp of current datetime
Add extra tests for this mode
Tracked via #72
