Add marketplace giphy enhancement

I think it'd be fun to add the giphy enhancement to our rocket chat.
Who's with me? :D

Pro's:
- FUN!
- People will be more prone to use Rocket Chat instead of Slack if it has the same features

Con's:
- No testing has been done.
- External source, so prone to data leeks
- We need to use marketplace, which might leek some data to the Rocket Chat company. (need to figure out if this is true)