Fix misc. things

[Psirus]

• remove ENABLE_OPENMP
• remove ENABLE_CUSTOM_EXAMPLES
• correct naming of unit tests (some still had a forward slash in them)
• correct running of integration tests (unittests with "integration" in the name where also run, like "IntegrationTypeTensorProduct")
• less output during coverage report creation

[codecov[bot]]

Codecov Report

Merging #214 into PDE_reviewed will not change coverage. The diff coverage is n/a.

@@              Coverage Diff              @@
##           PDE_reviewed     #214   +/-   ##
=============================================
  Coverage         67.82%   67.82%           
=============================================
  Files               312      312           
  Lines             12089    12089           
=============================================
  Hits               8199     8199           
  Misses             3890     3890

Flag	Coverage Δ
#integrationtests	46.5% <ø> (-0.64%)	:arrow_down:
#unittests	77.82% <ø> (ø)	:arrow_up:

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