AbiWord Import filter

Change-Id: I90dc115044e5f81fa3a2b105d30d7d39e438b086
Reviewed-on: https://gerrit.libreoffice.org/7411
Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>