Add feed_url to feeds

Need to separately store url and feed_url
Refactor feed model and feed parser

Use class level methods for all methods in FeedParser
Refactor Feed model
Fix loading by api_key
Refactor feeds controller for API
Use Sanitize gem
Create new Scrubber class

Delegate methods to scrub article data, can also be used to scrub other
attributes. Set whitelist attributes within HTML module for use
elsewhere.