Allow scaling the code editor's font size

[Rekkonnect]

Shortcuts: Ctrl + Mouse wheel and Ctrl + (+/-).
Also display this setting in the settings view.

Save the font size as a setting and remember upon restarting the program. Only save the setting when the user stops scaling for 1.5 seconds to avoid saving the settings on every intermediate scroll. Notify that the font size setting was saved with a custom toast message.