logilab-common #294479 use more standard source layout [validation pending]

- put sources under logilab/common in the source tree instead of directly in the toplevel directory
- declare logilab namespace
- use setuptools instead of a dual setuptools/distutils build system

prioritynormal
typeenhancement
done in1.0.0
load5.000
load left0.000
closed by#6db240fd8b0c [pkg] pure setuptools setup.py (closes #294479)
patch[pkg] pure setuptools setup.py (closes #294479) [applied][layout] change the source directory layout [applied]