[SRU] libreoffice 5.4.5 for artful

[Impact]

 * LibreOffice 5.4.5 is the fifth bugfix release of the still 5.4 line. Version 5.4.4 is currently in artful-proposed.
   For a list of fixed bugs compared to 5.4.4 see the list of bugs fixed in the RC1:
     https://wiki.documentfoundation.org/Releases/5.4.5/RC1#List_of_fixed_bugs

 * Given the nature of the project, the complexity of the codebase and the high level of quality assurance upstream, it is preferable to SRU a minor release rather than cherry-pick selected bug fixes.

 * Libreoffice 5.4.5 fixes CVE-2018-6871

[Test Case]

 * CVE-2018-6871 should be verified to be fixed

 * No other specific test case, bugs fixed upstream hopefully come with unit/regression tests, and the release itself is extensively exercised upstream (both in an automated manner and manually) by a community of testers. Each minor release usually goes through two release candidates, but 5.4.5 was initially unscheduled and it had a shortened cycle (only a single RC).

 * The libreoffice packages include autopkgtests, those should be run and verified to pass.

 * General smoke testing of all the applications in the office suite should be carried out.

[Regression Potential]

 * A minor release with a total of 69 bug fixes always carries the potential for introducing regressions, even though it is a bugfix-only release, meaning that no new features were added, and no existing features were removed.

 * A combination of autopkgtests and careful smoke testing as described above should provide reasonable confidence that no regressions sneaked in.