Forge documentation: rename 7.10 references to CMS 10

At most standard plugins, the forge documentation has two notes that development has moved to 7.10 instead of just 10.

See at http://taxonomy.forge.onehippo.org and http://taxonomy.forge.onehippo.org/build-demo.html

This is already fixed at http://ecm-tagging.forge.onehippo.org and http://ecm-tagging.forge.onehippo.org/build-from-source.html

Let's check all other standard plugins!