Fix wrong redirect after featured/unfeatured article

## PR summary
This PR fix the small issue #4834 reported by @clausw. When you go to Content -> Featured articles, click on star icon next to each article to feature/unfeature it. After change is made, instead of going back to Featured articles page (which display list of featured article), you are redirected to standard articles page (which display all articles).

The reason of this error is because the redirected url is hardcoded in the code. I just change the code alitle to redirect users back to the correct view.

I also fixes some code styles of the file administrator/components/com_content/controllers/articles.php as well

## How to test

1. Go to Content -> Featured articles, change status of an article to make it featured/unfeatured. Make sure that you are redirected back to featured articles page after the change is made

2. Go to Content -> Articles Manager, change status of an article to make it featured/unfeatured. Make sure you are redirected back to  Articles Manager page after the change is made.