Merge branch 'issue/mixed_type_fieldmatvec' into 'develop'

Redesign of FieldMatrix + FieldVector arithmetic operations

See merge request !83
4 jobs for develop in 37 minutes and 28 seconds (queued for 2 minutes and 9 seconds)
Status Job ID Name Coverage
  Test
passed #8428
debian:10 clang-6-libcpp-17

00:28:33

passed #8427
debian:10 gcc-8-17

00:17:59

passed #8429
debian:9 gcc-6-14

00:18:46

passed #8430
ubuntu:18.04 clang-6-17

00:25:43