Add bots!

[feross]

Let's test out using bots to help us with issues. I added these to the WebTorrent repo and they're working great!

• ProBot Request Info (https://probot.github.io/apps/request-info/)
  • Follow up when a user opens an issue/PR with no description
• ProBot Welcome (https://probot.github.io/apps/welcome/)
  • Welcome users who open their first issue/PR
• ProBot Lock (https://probot.github.io/apps/lock/)
  • Lock threads that have been closed and have no activity for 180 days to prevent random drive-by comments
• ProBot No Response (https://probot.github.io/apps/no-response/)
  • Close issues that have "need more info" label after 7 days with no response from issue opener
• ProBot Stale (https://probot.github.io/apps/stale/)
  • Mark issues with no activity in 90 days with a "stale" label and leave a comment, then close the issue if there's still no activity 7 days later. Issues with the "accepted", "enhancement", or "bug" label will never be marked stale.
• ProBot WIP (https://probot.github.io/apps/wip/)
  • Prevent merging of PRs with "WIP" in the title