logger and option of using IssuesLogger

InstagramReporter#logger and option of using IssuesLogger (or any other logger, which responds to debug, error etc)
These could be simpler (just `logger.debug(....)) when we had all classes  "namespaced" with some common module name for all gem classes (i.e. `InstagramReporter`). 
This would be a good idea in general, not only for this reason.