Add greater time resolution to contact log

[adamfowleruk]

Contacts.csv file currently logs down to the second. For multiple readings from the same device over the course of a single scan this isn't recording at a granular enough level to maintain order and frequency of readings in analysis of the data post-recording.

Modify the contacts.csv logger to log down to the millisecond using YYYY-MM-DD HH:mm:ss.SSS.

Also then verify that ConcreteBLEDatabase and ScanResult are contemporaneous with each other, and no significant or skewing artificial delay is being introduced by this code.

Note this is not an issue for casual use of Herald, but when performing very detailed post-recording data analysis this level of granularity becomes desirable. Only affects the demo app, not production applications (which have access to the full Date class and its level of accuracy, rather than a textually rendered time).