Also fix a handful of segfaults caused by improperly retained byte slices
from bolt, and combine two view transactions into one to avoid data
race when a delete happened between them.
More specifically, introduce a `scheduleAfter` argument to
Store.CreateTask. The previous behavior was leaving a new task's meta
LatestComplete value set to zero, which meant that the first run of a
schedule would start from 1970. Now, it's set to time.Now unless
otherwise specified.
Updates #595.
Lyon Hill
Mark Rushakoff
Michael Desa
Leonardo Di Donato