[cwconfig] drop importing legacy cubes
This finally drop support for legacy cubes.
In cwconfig, don't load modules in the "cubes" namespace.
In cube_pkginfo() handle CW_MIGRATION_MAP which wasn't working with new style cube.
Drop all method specific to legacy cubes importer: cubes_search_path(), extrapath(), cls_adjust_sys_path()
Drop environment variables related to legacy cubes: CW_CUBES_PATH and CW_CUBES_DIR
[MASTER]
load-plugins=cubicweb.pylintext
ignore=__pkginfo__
[MESSAGES CONTROL]
disable = too-many-ancestors,too-many-instance-attributes,too-many-public-methods,
too-few-public-methods,too-many-arguments,import-error
[BASIC]
function-rgx = [a-z_][a-z0-9_]{2,35}$
good-names=w,_
[TYPECHECK]
generated-members=debug,info,notice,warning,error,critical,exception
[CLASSES]
exclude-protected=_cw,_cnx,
# namedtuple public API.
_asdict,_fields,_replace,_source,_make
[FORMAT]
max-line-length=100
max-module-lines=2000