Fisrst of all, who are not that bright and have no clue what I'm writing about, let me show you what are these three-dot menu button.
These buttons are set as default in newer devices containing only three buttons - home, menu and back button. Therefore, the menu button has no room there and needs to be put somewhere else - on the screen.
As the name suggests, this button is indicated as three-dot button mostly appears in upper corner of the app.
Credits go to c3k@XDA
Basically, the menu button is not that popular on newer devices such as N4/7/10 thanks to software keys.
These devices automaticlly recognizes the menu button's missing and create a one.
Therefore is no need to put this menu button in apps. But if you own an older device missing the software keys (even the newer ones hasn't them) such as Galaxy S2, or even S3 and S4, you can manually enable this option in case you want remap the menu button.
This mod is pretty simple and is XPOSED. That means you have to get the XposedFramework (It's easy, don't worry) HERE.
To activate the mod, just enable it in modules section and reboot your phone to take the effect.
The mod should work on every phone, the code is not that hard - It's only disabling and using 0 height of navbar.
Anyways, it has a tiny bug - see the picture below:
After setting the height to 0, Samsung apps use fixed layout and makes it kinda' buggy - it creates a blank room showing nothing..
Even it's a little mod that should not harm or brick your device, backup your ROM&data before installing it.