Feature/interpolation3 d

This branch adds a simplified/memory-optimized version of the Shepard algorithm to enable interpolatin of 3D data. For 1D-data, the original quadratic/linear algorithm are chosen automatically. In addition, the weights are stored for each point, which might be useful for e.g running the same interpolation multiple times in future implementations.

It also moves the pts field logic from FieldConvert into LibUtilities so it can be used from all over nektar and enables Equationsystem::EvaluateFunction to handle .pts files, too.

After the merge of the feature/FieldConvertEquiSpaced branch, two new regression tests were added to ensure the equispacedoutput and the isocontour modules work as expected.