[linearelliptic.discretizations.block-swipdg]

Added first draft of estimate(). Does the same as the estimator from
linearelliptic.discretizations.swipdg with the slightly worse local
summation atm.
[examples.linearelliptic.block-swipdg] added error estimation
[lib] removed everything we do not need for the moment
[linearelliptic.discreteproblem] update multiscale grid visualization
[linearelliptic.discretizations.block-swipdg] implemented estimator
[tests.linearelliptic-swipdg] do not use

DUNE_HDD_LINEARELLIPTIC_DISCRETIZATIONS_SWIPDG_ESTIMATOR_ALTERNATE_SUMMATION
[examples.linearelliptic.block-swipdg] define

DUNE_GRID_MULTISCALE_PROVIDER_CUBE_DISABLE_CHECKS
[cmake] disabled everything exect the one test and example of interest
[examples.linearelliptic.spe10model1] added first draft
[lib] readded the CG discretization
[cmake] added examples.linearelliptic.spe10model1
[linearelliptic.discretizations.base] updated exception
[linearelliptic...block-swipdg] expose local discretizations
[linearelliptic...block-swipdg] added first draft of estimate_local()
[examples.linearelliptic.spe10model1] finished infrastructure
[examples...spe10model1] fixed setup
[examples...spe10model1] added some more output
[linearelliptic...swipdg] replace fem_localfunctions by fem
[linearelliptic...block-swipdg] replace fem_localfunctions by fem
[tests.linearelliptic-swipdg] replace fem_localfunctions by fem