Replaced String with OUString in mediawindow.cxx, basdoc.cxx,
basdoc.hxx and bastype3.cxx. In other files I only replaced,
what was necessary for the changes in basdoc to work.

Change-Id: I1ad0e7e262f8becdf57f182853aaa914a88895a4
Reviewed-on: https://gerrit.libreoffice.org/2554Reviewed-by: Muthu Subramanian K <muthusuba@gmail.com>
Tested-by: Muthu Subramanian K <muthusuba@gmail.com>