new Feature: Create dumps with MathML

new plugin for export that installs a new filter called mathml

fix: adjustments to the new version of the math extension in
the ReRenderMath script

added: missing database functions for calculation of distances
used in the CalculateDistances script
(still open: write install script for these functions)

Change-Id: I94749bafb9b0f94a62e517c748ee416368d2eecb