Fix feed ordering

[aledeg]

Closes #4790

Changes proposed in this pull request:

• sort feeds in category in a consistent manner.

How to test the feature manually:

1. Check the feed order within a category in the subscription page
2. Validate that the order is the same in normal view
3. Validate that the order is the same in global view

Pull request checklist:

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

Additional information can be found in the documentation.

Before, the feeds were not ordered every time there was a change in the category feed list. This behavior was causing discrepancies in the displayed list. Now, the feeds are ordered every time there is a change in the category feed list.

[math-GH]

I am not sure if it is the best way. Isn't there a chance to have the ordering while fetching the data in the database request (SQL query)?

[aledeg]

Probably. But if you do that you have to take into account that we are supporting 3 different databases with their own syntax. On top of that, I am not sure they all supports sorting the same way. The sorting was already in the category class. I figured it was the most appropriated location to add it.

[aledeg]

I've checked the differences between the 3 databases and I could not find something that is reasonable. We also supports adding a feed without putting it in the database (addFeed method) which will void the database sorting.