Replace master with the 2.10.x-dev branch of the schema plugin

Master is an outdated branch of which the only commit was the base iso19139 schema plugin. The 2.8.x-dev branch was then created to track GeoViQua-related changes before being merged back into master. As it was never merged back and a 2.10.x compatible version of the plugin has since been developed, let the 2.10.x-dev branch now become master.