Add fix for epoch dates

[atruskie]

Various sensors have an internal epoch (start of time) that differ.

When their clocks are not configured correctly those epochs are emitted as the date. This is faulty data which should be detectable.

• Create well known problem to document this effect
• Create a non-fixable fixer for this
• Consider creating a redate feature: the first date of a recording session is assumed to be wrong, but assuming the sensor's internal clock is accurate we can 'add' the date of the recordings onto the relative spacing between the datestamps. This is possible if the user has some other information about the start date of the deployment.