Rename problem file 'wriggers-l-shape' to 'identity-deformation'

Because that is what it is: It implements the identity deformation
for three-dimensional continua.

The name 'wriggers-l-shape' refers to a simulation that appeared in

  O. Sander, P. Neff, and M. Bîrsan: Numerical Treatment of a
  Geometrically Nonlinear Planar Cosserat Shell Model, (2016)

It belongs to the dune-gfe module, and only got into dune-elasticity
by accident.

problems/film-on-substrate-deformation.parset

@@ -115,7 +115,7 @@ mooneyrivlin_energy = square # log, square or ciarlet; different ways to compute
 #  Boundary values
 #############################################
 
-problem = wriggers-l-shape
+problem = identity-deformation
 
 ###  Python predicate specifying all Dirichlet grid vertices
 # x is the vertex coordinate

problems/finite-strain-elasticity-bending.parset

@@ -56,7 +56,6 @@ baseTolerance = 1e-8
 
 energy = stvenantkirchhoff
 
-## For the Wriggers L-shape example
 [materialParameters]
 
 # Lame parameters
@@ -79,7 +78,7 @@ mooneyrivlin_12 = 0
 mooneyrivlin_03 = 0
 
 mooneyrivlin_k = 1e+6	# volume-preserving parameter
-mooneyrivlin_energy = log # log, square or ciarlet; different ways to compute the Mooney-Rivlin-Energy
+mooneyrivlin_energy = log # log, square or Ciarlet; different ways to compute the Mooney-Rivlin-Energy
 
 []
 
@@ -87,7 +86,7 @@ mooneyrivlin_energy = log # log, square or ciarlet; different ways to compute th
 #  Boundary values
 #############################################
 
-problem = wriggers-l-shape
+problem = identity-deformation
 
 ###  Python predicate specifying all Dirichlet grid vertices
 # x is the vertex coordinate

problems/wriggers-l-shape-dirichlet-values.py → problems/identity-deformation.py

@@ -2,17 +2,7 @@ class DirichletValues:
     def __init__(self, homotopyParameter):
         self.homotopyParameter = homotopyParameter
 
-    # Deformation of 3d classical materials
+    # The identity deformation of 3d classical materials
     def dirichletValues(self, x):
-        # Clamp the L-shape in its reference configuration
+        # Clamp the shape in its reference configuration
         return [x[0], x[1], x[2]]
-
-    # Deformation of Cosserat shells
-    def deformation(self, x):
-        # Clamp the L-shape in its reference configuration
-        return [x[0], x[1], 0]
-
-    # Orientation of Cosserat materials
-    def orientation(self, x):
-        rotation = [[1,0,0], [0, 1, 0], [0, 0, 1]]
-        return rotation