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

Directories dep

Print API check to console instead of stdout

Add bevy_console

Fix comment

Start of API mod and connection check plugin

Small comment

lightweight futures and reqwest blocking deps

Move menu to plugins mod

Reqwest and serde deps

Move Cfg things to a new mod

Create plugins mod, move splash to plugins

Move user cfgs to CfgUser