If the user edits an embedded object it is converted to ODF, so we
really need to be able to store such objects.

Ensure that the proper MediaType is set in [Content_Types].xml,
the package relationship type in document.xml.rels and
the proper ProgID attribute in document.xml.

(cherry picked from commit 2a9f1dd2)
(cherry picked from commit 456d0315)

sw: replace OUStringBuffer

(cherry picked from commit ea50cb70)
(cherry picked from commit a0cad01e)

sw: fix MSVC build, stupid thing can't initialize const members

(cherry picked from commit 159e7879)
(cherry picked from commit 0050019b)

Change-Id: I3c78c5ab5b4d534213af5e773fe0c6c2c92d9104
Reviewed-on: https://gerrit.libreoffice.org/20759Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>
(cherry picked from commit 0d5c9007)