Features/time data

Closed username-removed-200434 requested to merge features/TimeData into develop
  1. DifferentialOperations (former RegularFieldDifferentialOperations) processes time data: spatial operations (grad... div/rot) can operate on all time moments, time differentials (d/dt and d2/dt2) introduced. Time differentials can be computed for irregular time dependent fields.
  2. LineSlice operates on time data
  3. New options in RegularField module
  4. Some small cleanups (e.g.VNLogo)