Improving custom Key-binds

[ZERICO2005]

Is your feature request related to a problem? Please describe.
Custom Key-binds are not too great for the moment. Under the hood, Key-binds only rely on telling if a key is pressed or not, instead of also responding to key-up and key-down events. There is also no option to bind the mouse buttons to anything.

Describe the solution you'd like
Re-implementing the custom Key-binds to allow for responding to more types of key events (Such as key-up and key-down); Adding support for mouse button bindings; supporting Shift/Ctrl/Alt as modifiers; and possibly switching to SDL_KeyCode.