Merge branch 'feature/heat-equation' into 'master'

CHANGELOG.md

doc/doxygen/modules.txt

dumux/common/pointsource.hh

dumux/porousmediumflow/CMakeLists.txt

dumux/porousmediumflow/nonisothermal/iofields.hh

dumux/porousmediumflow/solidenergy/CMakeLists.txt

dumux/porousmediumflow/solidenergy/localresidual.hh

dumux/porousmediumflow/solidenergy/model.hh

dumux/porousmediumflow/solidenergy/volumevariables.hh

test/porousmediumflow/CMakeLists.txt

test/porousmediumflow/solidenergy/CMakeLists.txt

test/porousmediumflow/solidenergy/main.cc

test/porousmediumflow/solidenergy/params.input

test/porousmediumflow/solidenergy/problem.hh

test/porousmediumflow/solidenergy/spatialparams.hh

test/references/test_solidenergy_tpfa-reference.vtu