[FEATURE] Add Customizable Shortcut System

[DeveloperPaul123]

With all of the actions that are possible now within fstl, it would be good to make these accessible via keyboard shortcuts. However, instead of hardcoding these shortcuts, we should instead create a system that allows users to assign whatever keyboard/mouse shortcuts they would like for a particular action.

The shortcut selections should be saved to user local storage and persistent across application sessions.