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

[uicfg] uicfg.py moves from web/ to web/views/ (prepares #2406609) We are about to make uicfg selectable. Registrable / selectable views and helpers live in web/views. Hence the move. Backward compat is put in place. However CubicWeb imports of uicfg are updated to the new location.

[appobject] introduce RegistrableObject base class (prepares #2406609)

[cwvreg] introduce lgc version 0.59 and remove unneeded method redefinition (prepares #2406609) The new logilab.common.registry makes this moot.

[BFSS] mark fs_imported value as uncachable This will finally fix the `test_bfss_fs_importing_transparency` pass again. Regression was introduced by 4ba11607d84a

[entity] add a "repo_side" parameter to `_cw_dont_cache_attribute` This parameter (defaulting to `False`) is used to inform cubicweb that we really really do not want to cache a value during creation or update. This will be used by a storage that may do very specific processing on attribute values that result in a stored value different than the provided one (e.g. BFSS `fs_importing` mode).

[merge] backport stable fixes

[entities] fix test failures introduced by fixes in workflow related message strings (completes 9bb93efa1952)