Define a compat MP for old theme modules

Repo created at https://github.com/nuxeo/marketplace-theme-compat

Should hold MP configuration, adding all modules from https://github.com/nuxeo/nuxeo-theme-compat, should also remove nuxeo-theme-migration.

Compat contributions from https://github.com/nuxeo/nuxeo-theme-compat/tree/master/nuxeo-theme-webapp-compat should also be reviewed: some default contributions will now be served by the wro servlet even when using old themes modules (see page_resources.xhtml code at https://github.com/nuxeo/nuxeo-theme-compat/blob/master/nuxeo-theme-jsf/src/main/resources/nxthemes/jsf/widgets/theme-view.xml).