make ui configurations selectable (closes #2406609) * introduce a new 'uicfg' registry (storing instances) * use the relevant new APIs from lgc.registry to manage the new registrable uicfg objects * cw event manager useage is gone; instead thze standard registry reloading mechanism is used * ensure i18n commands still work (devctl) * introduce dynamic uicfgs use whenever possible (various views), even though sometimes the classic 'static' usage remains

"""cubicweb-%(cubename)s application package

%(longdesc)s
"""