[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

### Requirements for tests in various cubicweb/**/test directories. ###

## shared by several test folders
docutils
webtest

## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails

## cubicweb/devtools/test
flake8

## cubicweb/hooks/test
psycopg2

## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth
repoze.lru

## cubicweb/sobject/test