Allow switching between races

[Pimentoso]

Prerequisite: #22

After races are saved each in a different file, we can have a function to switch between active races to allow multiple races to be ran the same day (different categories on the same track)

• Need to add a modal that asks for a race name when creating a new race

• Need a menu that lists races reading the files in the folder

• Maybe have an electron menu with a dropdown with recent files

• Implement a direct file>open function later

[Pimentoso]

Need to override all native application menus, so make a decent about dialog while at it.