Closes #

I have noticed that one of my feeds tries to perform an HTTP redirect while setting a cookie (some kind of spam/rate limiting thing I guess). Neither option is currently supported by FreshRSS, so I added them as advanced feed options.

Changes proposed in this pull request:

• Add the advanced feed options to allow cookies and HTTP redirects. Both are disabled by default.

How to test the feature manually:

1. When subscribing to a feed, open the "Advanced" settings menu and set the "Allow cookies" option, and a value of 5 for HTTP redirects;
2. Subscribe to the feed;
3. In the "feed" database table, check the "attributes" column. Observe the following attributes:
   1. "10031": "" (CURLOPT_COOKIEFILE)
   2. "68": 5 (CURLOPT_MAXREDRS)
   3. "52": 1 (CURLOPT_FOLLOWLOCATION)

A similar sequence of actions can be performed to manually test modification of these attributes on an existing feed.

Pull request checklist:

• clear commit messages
• code manually tested
• unit tests written (optional if too hard)
• documentation updated