1. Create an autohotkey script (e.g. alwaysontop.ahk).
  2. Add the following entries: 
    #^+t::
	WinSet, AlwaysOnTop, On, A
Return

#^t::
	WinSet, AlwaysOnTop, Off, A
Return

    Example script

    #NoEnv  ; Recommended for performance and compatibility with future AutoHotkey releases.
; #Warn  ; Enable warnings to assist with detecting common errors.
SendMode Input  ; Recommended for new scripts due to its superior speed and reliability.
SetWorkingDir %A_ScriptDir%  ; Ensures a consistent starting directory.

#^+t::
	WinSet, AlwaysOnTop, On, A
Return

#^t::
	WinSet, AlwaysOnTop, Off, A
Return

To make a window always on top press the following combination:

Win + Ctrl + Shift + t

To disable the effect of the always on top press the following combination:

Win + Ctrl + t