Fix Newton.

Conflicts:
	hermes2d/src/solver/newton_solver.cpp
Adjust Newton.
A fix in Essential BCs.
Update Newton.
Add some checking and code cleaning to Newton.
Update of DP cache.
Make some mixins methods virtual.
Progress on mixins, add reporting of DG cache hits and misses.
Fix cache.

Conflicts:
	hermes2d/include/discrete_problem/discrete_problem_cache.h
Fix in DP cache helper.
Intel compiler fixes.
Fix file's name.
Merge branch 'devel' of git://github.com/hpfem/hermes into devel
Removing old weakforms_neutronics.
Adding region-to-material mapping to neutronics weak forms.
Removing a warning message.
Improvement of the common SourceFilter.

 - the SourceFilter can now be defined for multiple fission regions
 - therefore, get_material() was moved to MaterialPropertyMaps, so that it is available also in the filter
 - SourceFilter now accepts a reference to MaterialPropertyMaps instead of pointer (I learnt that polymorphism works with either of the two and now it is more consistent).
SPN weak forms.
Updating the API of SPN neutronics weakforms.
Adding the first SPN example.

At this moment, it just displays the mesh.