feat($LogProvider): flag to allow hide/show of $log.info()/$log.log()

Add method to set a flag to enable/disable $log.info() and $log.log() messages.
**$logProvider.enableMessages(false|true)**
This is similar to how $logProvider.debugEnabled() works.

- I haven’t gotten the tests to pass yet, there’s an error in the logSpec saying $LogProvider undefined.