Allow Slack integration to define username vs "Ghost"


Right now, the Slack integration hardcodes the username to “Ghost”. It would be nice if one could define their own username to use vs “Ghost”. Could be a slack setting read from the database, much like the webhook URL. I tried to implement this myself by hacking the Ghost core, but it turned out to be a pretty daunting task. I’ll keep hacking at it, but if anyone has any good examples of someone hacking core with good documentation (specifically, adding migrations and changing db stuff), i would greatly appreciate it.