wav files for tests missing

[l0calh05t]

While the sources for the tests are included, the wav files required to actually run them are not.

[l0calh05t]

I found the test files at https://tech.ebu.ch/publications/ebu_loudness_test_set
It might make sense to download them automatically via a ExternalProject_Add.

[l0calh05t]

  include(ExternalProject)
  ExternalProject_Add(
    ebu-loudness-test-set
    URL https://tech.ebu.ch/files/live/sites/tech/files/shared/testmaterial/ebu-loudness-test-setv05.zip
    URL_HASH SHA256=9cc500b4df83f7c21855c74dce795ef5209a752bf884253ae57d0ce512efb062
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ""
    SOURCE_DIR ${CMAKE_CURRENT_BINARY_DIR}/ebu-loudness-test-set
  )

  add_test(
    NAME ebu-loudness-test
    COMMAND r128-test-library
    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/ebu-loudness-test-set
  )
  add_dependencies(r128-test-library ebu-loudness-test-set)