Better management for events

[desko27]

We need a clearer contract for the events, especially when dealing with them in the renderer process.

• Create enums for each event
• Maybe use this
• Consider building a class for events management, so an instance is "exposed to the main world" and can be used like an API client for events (a bag of known methods)
• Improve preload.js (and add types, although if the previous one is done it will be typed already because of the class)
• Move from window.electron to window.whatever, since the name electron is confusing because it's not actually electron but a custom API that is exposed in window from preload.js
• Add specific types in electron.d.ts for window.whatever (rename to whatever.d.ts too), importing specific event types (from original events file, or from @types) so event listeners provide intellisense in the renderer code (again, if a class instance is registered in preload.js we will only need to load that one to get the right typings)