Preparation for msh2vtu overhaul

mainly adding more meaningful tests for msh2vtu, also some cleanup here and there.

added Infrastructure tests - CI labels

requested review from @TobiasMeisel

assigned to @FZill

added 3 commits

• 947d11fb - [meshlib] move BHE meshing into separate file
• e4f349b0 - [msh2vtu] remove legacy files
• 6e18b00f - [tests] add tests which actually check the resulting meshes

Compare with previous version

approved this merge request

mentioned in commit f41d4bba

merged

changed milestone to %0.5.0 Release