Enumerable Dynamic Field Maps and Globalisation of Local Fields

Summary:
Fied maps can now have a dynamically determined number of components. Indispensible for using large fields (e.g., per slip system values) with Python. Also: simplyfies I/O a lot.

Field maps now have an enumerate() method that returns an iterable proxy for the map. The iterates are tuples the pixel coordinate and the cell data.

CellBase and Cell can now return global fields into which local material fields (e.g., internal variables of the materials) have been copied. Very useful for I/O, and helpful for debugging.

Test Plan: Jenkins passes

Reviewers: afalsafi, RLeute

Reviewed By: afalsafi

Differential Revision: https://c4science.ch/D199