DirectoryEngryReference: Adds blank class file

This commit starts the new directory entry reference parameter type.

This commit also adds the starting test suite, and tests to make sure
the class isn't deleted by somebody on accident.

Signed-off-by: Mark Stenglein <mark@stengle.in>
1 job for 3-dir-entry-ref in 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #2328
test_lib-ical

00:00:25

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