Re-align a data set to GPS time

[sprinkjm]

Given a CAN_Messages and a GPS_Messages tuple, re-export the CAN_Messages as aligned with GPS time (rather than system time).

Care should be taken to avoid out-of-order realignment, or jumps in data time. This may be related to strym_notebooks#1 in terms of how much the data drift over time.

Many of the initial challenges will be off by 3600 seconds. For the first pass here, simply remove by the largest offset seen between GPS time and system time---which is assuming that GPS time will never bee too early, only too late, with respect to system time errors.