New JLBP - Libraries should not expose unnecessary implementations in dependency tree.

Libraries should use API interfaces as much as possible. In terms of logging, depend on Logging API interfaces (e.g., slf4j). However, in order for slf4j to print out the log somewhere, it requires a binding (e.g., slf4j-log4j). The binding (implementation) should not be exposed to library consumer via transitive dependency. Bindings/implementations such as this should be set as `optional` so that it doesn't expose to the user depending on this library.