[space...fem-localfunctions] minor update
[playground.space.raviartthomas...] update
* add static checks
* update to fulfill interface
[space.raviartthomas...] moved out of playground
[tests.spaces] added raviarthomas
[tests.elliptic-testcases] update ESV07
* use exactly the same grid as in the publication
[assembler.gridwalker]
* call codim 1 functors with inside and outside entity
* adden combinde codim 0 and 1 functor
[assembler.system] updated codim 1 functors
[discretefunction.default] updated visualization
* make subsampling optional
* delegat work to base type
[discretefunction.default]
* allow to get a const local discrete function from a non const function
[functional.base] update apply_local() signature
[localoperator.codim0] allow to specify additional integration order
* will be added to the automatically computed order of the integrand
[product.interfaces] simplify apply2() for vectors
[product.elliptic] added first draft
* behaves like H1 semi for diffusion == 1
[operator.interfaces] some operators are products
* derive OperatorInterface from ProductInterface, implement apply2()
  for vectors and discrete functions
* derive AssemblableOperatorInterface from AssemblableProductInterface,
  implement apply2() for vectors anf discrete functions
[operator.projections] let DirichletLocalizable fulfill product interface
[operator.oswald] added first draft
* added OswaldInterpolation from elliptic estimator test, seems to work
  but is untested and inefficient
* added first draft of OswaldInterpolationLocalizable, does not work yet
[tests.operator_oswald] added first draft
* does not do anything useful yet, just shows off the general usage
* refs #268
[tests.elliptic-discretizations] avoid name clashes
[tests.elliptic-testcases] order 2 is enough in ESV07
[tests.elliptic-testcases] whitespace