support logger group when refresh by the /refresh endpoint

[xfrogcn]

The current implement of LoggingRebinder , when refreshed by the /refresh endpoint, only changes the level of specific loggers and does not yet support changes the level of logger groups. This pull request adds support for logger groups in LoggingRebinder, including:

1. Modify the log level of the logger group
2. Dynamically add, modify, delete logger groups or loggers in groups

[pivotal-issuemaster]

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[spencergibb]

The constructor change is a breaking change, meaning this wouldn't be able to be included until next year. It seems like some of the changes go beyond groups setDefaultLogLevel(). Can you describe what those do?