Logger refactor: pluggable logger [WIP]

[EmilianoSanchez]

Javascript commons library

Changes:

• String constants were replaced with number codes, to support pluggable loggers for size reduction.
  • In case the log level is dynamically changed (via factory.Logger.setLogLevel method or initialState in local storage) and the provided Logger is not "compatible" with that log level, the logger will log the message code number anyway.
• Pluggable logger validator logs an error instead of throwing one if the provided debug object is not valid. It is done this way for consistency with the builtin logger validator, which logs en error if the provided debug value is not a valid string or boolean value.

To discuss:

• should we log a warning if dynamically changing the log level to a lower one that the one provided at settings? (e.g.: '[WARN]: lowering the log level from the one initially provided results in some logs without detailed description`).
• should we support boolean and string types for debug config anyway, but warning about the no detailed log messages?

[EmilianoSanchez]

Duplicated: #12