Add overload for LagrangeBasis with single node

examples/CMakeLists.txt

examples/boundary.cc

examples/convection_diffusion.cc

examples/ellipt.cc

examples/heat.cc

examples/init/boundary.dat.2d

examples/init/cahn_hilliard.dat.2d

examples/init/ellipt.dat.2d

examples/init/ellipt.dat.3d

examples/init/heat.dat.2d

examples/init/surface.dat.2d

examples/neumann.cc

examples/periodic.cc

examples/surface.cc

src/amdis/ProblemStat.hpp

src/amdis/ProblemStatTraits.hpp

test/ExpressionsTest.cpp

test/IntegrateTest.cpp