Post filtering by domain, flair and type

[Watchful1]

Replaces #7, #31, #49 and #66.

Rather than subscribing to an author, allow subscriptions to:

• Self posts
• Link posts
  • A regex filter on the link
• For both
  • Filtered by flair
  • Filtered by author
  • Filtered by author type (moderator/admin)
  • No filter, notify on all posts in sub

And a way to set defaults on a per sub basis.

[Watchful1]

https://github.com/TheDarkLordSano/HFYBeetusBot/search?utf8=%E2%9C%93&q=IGNORE&type=

[Watchful1]

Also filter if there is no flair

[Watchful1]

Flair filtering is done in theory. Going to wait till I have a few hours to watch the logs to actually update the bot since we risk filtering out everything if something goes wrong.