Add shortcuts to move current tab to left or right(previous or next)

Really don't like rearranging the tabs WITH MOUSE :(
I want to do that just like most tiling window managers do(awesome, Xmonad, qtile, etc.), so added these two functions:
Press \<a-k\> to move current tab to right(moveToNextTab).
Press \<a-j\> to move current tab to left(moveToPreviousTab).