UNO to CMIS properties conversion fix

The initial code always extracted Strings from the UNO instead of extracting
the same data type that was written into it. This patch extracts the
properties according to their data type and formats them to be reconstructed
into CMIS properties.

Change-Id: Ib160020e9d923a46e2c4f90924da847f2dac5e7a
Reviewed-on: https://gerrit.libreoffice.org/10586
Reviewed-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>
Tested-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>