Improved logging (issue #152)

[cmfabbri]

Replaces print() statements with logging calls, and integrates the dingo and bilby loggers so that both write to the same log file.

Changes:

• dingo/core/utils/logging_utils.py - updated; sets up a "dingo" logger that shares bilby's file handler when bilby is available, falling back to a standalone file handler otherwise
• replaced print() calls with logger.info() or logger.warning()
• files in dingo/pipe/ now use logging.getLogger("dingo.pipe") instead of bilby_pipe's logger
• print() kept in ls_cli.py, asimov.py (dryrun blocks) and main debug blocks

[stephengreen]

You should make sure that the creation of the logger is consistent with what @hcampe is doing with hydra.