Updating MySQL distance calculations to use metric (#921)

MySQL geo distance calculation functions currently return results in miles instead of kms. Multiplying result of function by 1.609344 should fix the issue.

Dev Note: Tested with a few situations with the report search and report view pages, which seems to yield the correct results. However, I'm not entirely confident I was able to explore all use cases for the Incident::get_incidents() and Incident::get_neighbouring_incidents().