Finish register/login, load configs on startup

Create a constants file

sl changes and fixes

Change CfgHidden to CfgDev

Move register/login to plugins, implement mostly

APIError struct and login/register API calls

Generic functions for saving and loading

Constants for Cfg filenames

Serde for Cfg structs

Serde for Cfg structs

New CfgUser fields

Add ProjectDirs resource

Print API check to console instead of stdout

Add bevy_console

Fix comment

Start of API mod and connection check plugin

Small comment

Move menu to plugins mod

Move Cfg things to a new mod

Create plugins mod, move splash to plugins