Currently, imported formulas use default Math object's margins,
that are 2 mm left & right for embedded object and 1 mm left & right
for its model. Before commit eae2331f,
there was also 3.5 mm bottom margin for embedded object.

This commit sets all margins to 0.
Unit test is included.

Change-Id: I23c78d4cedaeba8f2a70a000dca8e31de20bcab2
Reviewed-on: https://gerrit.libreoffice.org/32334Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>