oox: add a method to dump a PropertyMap as data

It was already possible to dump a PropertyMap as code, but not as data.
The plan here is that if we dump the customshape preset definitions as
data, then once there is a parser for it, we can get rid of the ugly
generated code.

Change-Id: If596941fedf71693e5d0bff436446ac0855c4c84
oox: add --data switch to generatePresetsCXX.pl

generatePresetsCXX.pl (as its name says) by default generates C++ code,
but with the new switch it filters out data from the provided
custom-shapes.log.

Change-Id: Ic59c666422db667112c280716f98342fabdae692