Discord Bot, Review function, Rewards, logging

- Curators now have the choice how they want to curate:
* By using a !command in a Steemit comment from their personal account
* By using a !command followed by a valid steem URL on Discord (new)
* By adding an emoji reaction on Discord to any link message (new)
- Users who received a bot comment can comment with !tfreview to ask for manual review to appear in the Discord feed
- Finished stream_rewards function (still testing before implementing automated reward sending)
- Implemented proper logging