Currently platform build contains ant targets to run ConvertSchemaToHTML
for documentation purpose.

This adds as a first step a new mojo
tycho-document-bundle-plugin:schema-to-html that offers the same
functionality and should act as a base to further improve the brittle
manually maintained references the current process requires and already
allows to move things from the ant build to the maven build files.

(cherry picked from commit 4c276d9)