resolved fdo#72537 write <loext:fill-character>

... instead of <number:fill-character> but read both.

(cherry picked from commit 9f87de91cee05656808a98ab1bd65ad9509ef7df)

Also needed for this is:

xmloff: add a generic LibreOffice ODF extension namespace

XML_NAMESPACE_LO_EXT can be used for elements and attributes that are
not yet specified by OpenDocument.

(Change-Id: Id29392533d46f6592d964ce79c05ffefa4d69ebc)
Reviewed-on: https://gerrit.libreoffice.org/5419
Tested-by: Thorsten Behrens <tbehrens@suse.com>
Reviewed-by: Thorsten Behrens <tbehrens@suse.com>
(cherry picked from commit de9b067bd13ec6632b49c9683255bd3a1d7ae13e)

Change-Id: Ia620fad575782f6174a9ee5fbbd8b396b21948e3
Reviewed-on: https://gerrit.libreoffice.org/7014
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>