CYB-272 Item submitter gets points when another user comments on item

 * Activity entries created for original poster and for commenter (if they are not the same)
 * Uses new activity type ("GetAComment") which has an English string in config/locales/en.yml
Merge pull request #181 from coyote/commenter_scoring

CYB-272 Item submitter gets points when another user comments on item