[server] Reprase messages of db-check to avoid using "system" and "sources"
And rather mention "entity type table" and "entities" table, which are
clearer references.
from cubicweb.cwconfig import CubicWebConfiguration
def includeme(config):
appid = config.registry.settings['cubicweb.instance']
cwconfig = CubicWebConfiguration.config_for(appid)
config.registry['cubicweb.config'] = cwconfig
config.registry['cubicweb.repository'] = repo = cwconfig.repository()
config.registry['cubicweb.registry'] = repo.vreg