Feature/testingfuzzydata

See merge request !489

Fix/1p2c tests on next

See merge request !521

Fix/1p tests on next

See merge request !520

The name given for the threshold setting for the velocity did not coincide with the one
used in the reference solution. However, the threshold used here several orders
of magnitude larger than the maximum occurring velocity. There are actually discrepancies
in velocity of 1% with respect to the reference solution!

3p conduction and convection tests on next

See merge request !519

[freeflow][test] Fix BC in test_kovasznay

See merge request !518

* forgotten during introduction of new BCs

[staggered] Introduce new boundary types

See merge request !509

Fix/use tag dispatching for initial method

See merge request !514

* initial(const SubControlVolume& scv) does not exist anymore

* use two separate functions for box and cc
* avoid compiler error if user wants to set the initial(const Vertex& v)
  or initial(const Element& e) method (for box or cc) explicitly in the
  problem instead of using initialAtPos

Merge branch 'postprocessing/exportscreenshot' into 'next'

See merge request !513

[postprocessing] Add pvpython script to export 2d screenshots

See merge request !510

Merge branch 'fix/handbook' into 'master'

See merge request !512

[doc] Remove section about outdated highlighting file

See merge request !511

* Allow to set a fixed value for a cell at the boundary directly
  instead of setting a value for the face

Feature/staggered energy

See merge request !483

Cleanup/staggered energy

See merge request !507

* for stokesni-condunction test

* ni tests are now in staggered folder

* so additional clean-up

* use correct distance to calculate temperature gradient
* do not multiply by sign of unit outer normal

* free flow volvars now do the same as the porousmedium volvars concerning
  temperature and enthalpy

* add non-isothermal properties

* similar to mpnc now

* similar to mpnc now