Material as a string

This is a big change to almost all the build files to deal with
materials as a string, instead of a number. That needs two things, first
that I have added MaterialSupport.h and MaterialSupport.cxx, that give a
complementary function EvalMat which is similar to EvalVar.

Second every use of EvalVar<int> to get a material or similar needed to
be changed.

Note I have not actually started putting many of the materials in as
names. [Just a couple in ess and ts1 to test.]
Futher improvements to fix tiny issues with the material as a string
-- bug that allows a 0 material to be written
-- plate variables
Merge https://github.com/SAnsell/CombLayer into MaterialString
Merge branch 'MaterialString' of https://github.com/SAnsell/CombLayer into MaterialString