Class: output_controller  - X-Ref

This class decides, based in environment/backup controller settings about
the best way to send information to output, independently of the process
and the loggers. Instantiated/configured by @backup_controller constructor

Mainly used by backup_helper::log() (that receives all the log requests from
the rest of backup objects) to split messages both to loggers and to output.

This class adopts the singleton pattern to be able to provide some persistency
and global access.