renamed DOFVectorConstView into DiscreteFunction and added some more interpolation methods

4 jobs for feature/dofvector_global_evaluation in 20 minutes and 37 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #6885
debian:10 clang-6-libcpp-17

00:20:36

passed #6884
debian:10 gcc-8-17

00:15:14

passed #6886
debian:9 gcc-6-14

00:13:11

passed #6887
ubuntu:18.04 clang-6-17

00:19:15