Add option to read in a displacement file that will be used for the stress-free configuration of the shell elements
When startFromFile is set to true, then the stress-free configuration is read from the given file - this file needs to match the *finest* level of the grid
When startFromFile is set to false, the stress-free configuration can be given in as a function

Up until dune-common 2.7, the Dune namespace contained shared_ptr:
First as an actual implementation, later simply as a namespace
import.  Dune-common post-2.7 has removed that import,
and users of shared_ptr really have to explicitly specify
the std:: namespace prefix.

The predicates do implement operator(), so let's use that.

Previously, they all inherited from LocalGeodesicFEStiffness,
which was weird, because none of them implemented first or
second derivatives as you would expect from something called
'stiffness'.

Added program to solve a combined minimization problem:
Minmize the sum of an elastic energy (representing the substrate)
and a cosserat energy (representing a thin film on the substrate).