web/application: instantiate the repository outside of CubicWebPublisher This improves decoupling and allows ``CubicWebPublisher`` user to choose which argument are used during ``Repository`` instantiation. In particular is allows caller to provide a ``TaskManager``. The `vreg` argument of publisher is made mandatory. See CubicWebPublisher docstring for details. Related to #2249513

import ConfigParser
try:
    undo_actions = config.cfgfile_parser.get('MAIN', 'undo-support', False)
except ConfigParser.NoOptionError:
    pass # this conf. file was probably already migrated
else:
    config.global_set_option('undo-enabled', bool(undo_actions))