Investigate using better display names for mouse bindings

[toebeann]

Mouse3 and mouse4 are, according to the Unity game engine, the side-buttons on the mouse, due the fact it users a 0-based indexing system.

Currently, these bindings simply get displayed as their names according to Unity, which confuses users who assume mouse3 is middle mouse, and makes the mod look like it's made a mistake.

Under the hood, SN uses the names "MouseButtonLeft", "MouseButtonRight" and "MouseButtonMiddle" for 0, 1 and 2, and it passes these to formatter which displays them as icons.

We should investigate the possibility that they may have internal names for other mouse buttons, and if so, we need to make sure we use them. If they don't, perhaps we should handle this ourselves? Even if we just +1 the binding numbers?