ENH: particleTracks - updated to include field data

The utility will now add field data to all tracks (previous version only
created the geometry)

The new 'fields' entry can be used to output specific fields.

Example

    cloud           reactingCloud1;

    sampleFrequency 1;

    maxPositions    1000000;

    fields          (d U); // includes wildcard support

STYLE: minor typo fix