[tests.spaces] refine test of basefunctionset
[tests.spaces] enable mapper and basefunctionset tests
[localevaluation.elliptic] added some explicit specializations
* otherwise the compiler can not select in case of 1d grids
[space.raviartthomas.ppdelab] added local_DoF_indices()
[discretefunction.default] give a suitable default for subsampling
[operator.darcy] compute locally for raviarthomas range
[operator.reconstructions] implemented diffusive flux for pdelab
[localoperator.codim0] fix perfect forwarding
[localevaluation.ESV2007] added first draft of DiffusiveFluxEstimate
[product.ESV2007] added first draft of DiffusiveFluxEstimate
[product.elliptic] updated local operator use
[tests.elliptic-swipdg...] added diffusive flux estimator