Use device ID instead of session ID for logging

• [BREAKING] Removed the $session_id parameter from DefaultLogMetadata::requestTrace - use the new
  DefaultLogMetadata::deviceIdentityLazy method instead to capture the device ID into the logs.
  The session ID was removed because reading from $_COOKIE does not provide a value on the user's first
  request, and other methods (e.g. session_id()) may not give an accurate value if the session cookie name
  is customised but the session has not been started at the time of logging.
• Add class to assign users a device ID cookie and provide the value for logging
• Add class to wrap accessing / setting / deleting cookies for injectability and testability
• Add helper method to get a DateTimeImmutable from a unix timestamp, in current timezone