Event log cleanups from feedback

[BenGardiner]

These changes resolve a host of issues raised during detailed review and feedback from a few of our TSPs:

• make Log Event multidayBasis optional in progress reviewed -- issue #177
• make Log Event comment optional and rename to disambiguate in progress reviewed -- issue #178
• Log Event: rename distanceLastValid → distanceSinceLastValidCoordinates in progress reviewed -- issue #180
• make distanceUnits apply across the Event Log object in progress reviewed -- issue #181
• Log Event location object: rename distanceFrom → distanceFromIdentifiedPlace in progress reviewed -- issue #182
• Log Event location object: rename directionFrom → directionFromIdentifiedPlace in progress reviewed -- issue #183
• Log Event: rename sequence → sequenceId to be consistent with other id-like fields in progress reviewed -- issue #184
• Log Event: rename state → eventRecordStatus in progress reviewed -- issue #185
• Endpoint name Dispatch Message Object_Get a Message Receipt by its ID may be too long. in progress reviewed -- issue #176
• Log Event: add _REDUCED set of eventType enums in progress -- issue #186
• support annotations and log events made by someone other than driver in progress -- issue #187
• add eventDateTime to Log Events in progress -- issue #188

See the 'files changed' tab for details. https://previewotapi.docs.apiary.io/# has been updated for a rendering.

This will be merged next Monday unless changes are raised in review.