[disc] Enable optional internal Dirichlet constraints

Closes #705

See merge request !1664

[test][1p] add convergence test

See merge request !1665

[facet][box] use correct distance vector for tpfa on coupling scvfs

See merge request !1663

This reverts commit eb294caf.
Therein, the reference solutions for the box-facet-coupling tracer tests
were changed after modifying the coupling flux assembly in the scheme.
This however only affected cases of tensorial permeabilities and
shouldn't have influenced the solution of the tracer test.
With the fixes on this branch the old reference solution can be reused.

Make test_vtk_staggeredfreeflowpvnames test less aggressive

See merge request !1662

[facet][tracer] adapt reference sol to improved coupling flux computation

See merge request !1660

[facet][box] make coupling fluxes consistent for tensors

See merge request !1659

[glue] check non-uniqueness of raw intersection geometries only if dim1 != dim2

See merge request !1656

[md][glue] Fixes change that changed the orientation of inside/outside

See merge request !1657

[box][fvgeom] avoid storing element pointer

See merge request !1658

To make the interface more clear this commit introduces a new
intersection interface and deprecates the old one.

The old inside(n) is replaced by targetEntity(n)
The old outide(n) is replaced by domainEntity(n)
The old neighbor() is replaces by
numTargetNeighbors()/numDomainNeighbors().

Furthermore num{}Neighbors returns 1 if the {}-dimension is
smaller than the other dimension.

[shallow water] Add friction laws (Manning and Nikuradse)

Closes #688

See merge request !1596

Feature/optimize projector

Closes #708

See merge request !1646

Dennis Gläser authored Jun 27, 2019 and Timo Koch committed Jul 01, 2019

This way, a user can get access to the matrices underlying an
l2-projection. The projectors do not allow access to these matrices and
internally use a reduced matrix in case the target domain occupies a
larger geometric region than the origin domain, where the rows and
columns that correspond to dofs not taking part in the projection are
deleted.