[Feature request] Support Custom Mouse Bindings

[Rabcor]

Is your feature request related to a problem? Please describe.
Shortcuts cannot be bound to mouse buttons, and default mouse binds cannot be edited (for instance I want scroll to zoom, not change files, I want it to do something else)

Describe the solution you'd like
I would like to be able to bind mouse buttons in the shurtcut menu instead of just keyboard keys.

Describe eventual alternatives you've considered
An ability to bind mouse buttons in the config file and accompanying documentation/wiki entry on how to do so.

Context

I want mouse wheel to zoom in and out (and I do not want to press ctrl to do it, zooming on wheel is standard image viewer behavior in almost every other image viewer, so it won't be uncommon for users to want this), and I want the mouse side buttons to be able to switch to the next and previous files.

This would also make this PR unnecessary #152 (and that PR is a bad idea anyways because the back and forward mouse side buttons aren't always the same between mice)

[tsujan]

Personal preferences are considered up to a limit, beyond which, they only clutter the app.

[Rabcor]

Personal preferences are considered up to a limit, beyond which, they only clutter the app.

But being able to bind the mouse buttons is absolutely basic functionality, especially considering the application already has default mouse binds, it makes absolutely no sense to have mouse binds but make them completely unconfigurable...

Ah well, too much basic functionality is denied by devs at this point and issues like the gif aliasing are ignored because it only happens for some users, not all, guess this image viewer is a bust too, I'll try to find a better, more complete image viewer, it's hard though there is a surprising dearth of good image viewer and I was really hoping this could be it since there is so little additional functionality needed to make it perfect. If it comes down to it I might just fork it and fix it up myself it's so close...

Mouse bindings, gif playback quality, animated webp support, ability to pause gifs.... Those were the only things i found missing, it's really not a lot, only the animated webp support would potentially be non-trivial to fix...

Or maybe i'll go back to qimgv since the only thing holding that one back is bugs and it has everything i want.