Make logging more universal

[YuriVanWarmerdam]

Currently we use:

from rclpy import logging

logger = logging.get_logger(__name__)

But also:

from logging import getLogger

logger = getLogger(__name__)

In addition, sometimes the logger is a class member, and sometimes it is declared at file level.
All of this should be fair ly minor in tems of impact, since I am fairly sure it's all different ways of accessing the same singleton, but it's messy.

I propose we change all of these to to:

from logging import getLogger

logger = getLogger(__name__)

Always do this at file level, never as a class member. Main reason for this is that it reduces the extra "this.logger" syntax.