Hi okay so i've seen a lot of videos on youtube of "no-rooted" phones that have more icons in their multi-window bar, such as (Twitter, chrome, fb, kik messenger, kakao talk) but i've installed all this apps on my Note 2, and still can't see them on my bar.
Here is a thread which has a program(microsoft windows) to make almost any app become multiwindow without root. Any app that is modified in this way will not be updated. You can always get the newer apk and run it through the process again. [Tool] Add Multiwindow-option to almost every apk files - xda-developers