Set back this 20 MB default value for compatibility reasons

See also:
dbdacc73ae154237314d599194cc686bd738a9bf

This ten multiplier which was moved from the implementation
to the settings is live in the code only from 4.4 version, so
actually we can remove it without any problem, don't need to change
the default value on the UI.
I don't have any other reason to change that value so...

Change-Id: Ia17874cafeb013b89eedc300710392763c868f44
Test for linked graphic export / import of Impress

To avoid regression fixed by:
02b17c1bbdd19a978b9de646c0dacdad179c60de

It seems PPTX import is broken now.

Change-Id: I17228f4d8511b43d028b9ed8a6e77505e6143860
Test for linked graphic export / import of Calc

To avoid regression fixed by:
02b17c1bbdd19a978b9de646c0dacdad179c60de

Change-Id: Iaf2dea0cf221cb0e53debe4c1c611aab86dc29ff
Test for linked graphic export / import of Writer

Change-Id: Ib41921e9ceed30a05e16ace298d9c5dc87cc5458