Volocity: parse timestamps from .atsf files (rebased onto develop)



This is the same as gh-987 but rebased onto develop.

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See http://lists.openmicroscopy.org.uk/pipermail/ome-users/2014-March/004286.html and QA 7982.  Only one timestamp is stored per timepoint; each timepoint in the relevant dataset should be ~30 seconds apart.