Reword frontpage 'last thread' to 'last comment'

Previous: Last thread "Le Gank" written by kidkoma 3 days ago.
Current: Last comment 42 minutes ago in kidkoma's thread "Le Gank"
Don't slice comments (we need the last one's timestamp)
Merge pull request #18 from therealplato/patch-3

Reword frontpage 'last thread' to 'last comment'