added a Star System : starred items will be shown on the Starred Tab
Starred item will not be deleted by auto flush
improve navigation with starred/unstarred  items
improved starred/unstarred function, code refactoring using a mode
session var ('default', 'starred', 'history')
Merge branch 'starred' of git://github.com/MonsieurPaulLeBoulanger/miniflux into starred
Refactoring of bookmarks