make "Mark as read" OFF more persistent

continuation of commit 46b868a466
Now when "Mark as read" is manually unchecked this state is recorded in browser cookies and will survive page reloads,
so you do not have to keep un-checking "Mark as read" on selected articles after every "Mark these items as read" or page reload.
fixed formatting, replaced new tabs with spaces as in the rest of the file
Merge pull request #17 from neowit/master

Make "Mark as read" off state more persistent