Merge pull request #4954 from owncloud/fix-link-expiration-stable5

Backport of sharing fixes to stable5

* owncloud/fix-link-expiration-stable5:
  Calculate dateInPast and dateInFuture.
  Compare objects directly. Also use $expected and $actual.
  Add database tests for INSERT/SELECT date format.
  Add comment explaining how $dateInFuture was picked.
  Coding style: { for methods start are supposed to be on the same line.
  Expiration tests for sharing with groups.
  Do not repeat shareUserOneTestFileWithUserTwo() code.
  Make dates test class properties.
  Try to make Oracle happy by also specifying seconds.
  Test whether a still-valid user share is still accessible.
  Test whether an expired user share is still accessible.