Renames the 'karma' plugin to a 'points' system

Renames the 'karma' plugin to a 'points' system

Prior to this commit, rbot used a "karma" system for keeping
track of user points. This phrasing, while widespread, is
unnecessarily appropriationist.

This commit renames the plugin to a more neutral "points"
system, accomplishing exactly the same goal without using
culturally problematic language.

For more background please read: http://bit.ly/1MfLmce