reduce erroneous warnings in code style checkers (#1509)

* add a pylint config

- as generated initially using `pylint --generate-rcfile`
- added exclusion for `astropy.units` (all generated members fail erroneously for pylint)
- disabled rules for too-many-arguments and too-many-locals
- increase max parents from 7 to 9 (since Tool classes have 8 of them due to traitlets)
- added x,y,n to list of ok var names

* add per-file ignores for __init__.py

* add _v_attr* from pytables to allowed protected access

* reduce min-public-methods to 1