Fix reading a Gmsh file into a parallel UGGrid

Closes #553

See merge request !1385

[staggered] Add a bit of information on the staggered discretization.

See merge request !1366

Feature/improve wateroil test

See merge request !1388

[cleanup][flux] move cctpfa fourierslawnonequilibrium.hh from discretization to flux folder

See merge request !1384

[cmake] Replace optim.opts and debug.opts with cmake.opts

See merge request !1381

[test][2p] Attempt to improve the stability of the fracture tests

See merge request !1382

Depending on the Dune version, the boundary markers are present on
all processes (<= 2.6) or on the root process only (>= 2.7). Try to
handle this in a flexible way in the corresponding data handle:
Determine if the minimum size over all processes of the boundary
markers vector is zero. If yes, assume that the root process contains
all markers and broadcast them.

Currently, it isn't possible to refine a parallel UGGrid that has
been read by a GmshReader, see dune-grid issue #83. Therefore, don't
refine in the corresponding test.

[fix] Exception is not allowed in constepxr function

See merge request !1383

* Always compare the last vtu file
* Set maximum time step size lower
* Set Newton and linear solver tolerance lower

Feature/mpfa-scv-gradient-reconstruction

See merge request !1325

Feature/test facetcoupling xi

See merge request !1283