Initial Refactor (#3)

Overview:
* restructure repository to plugin as root
* Build.cs: remove redundant definitions, simplify library import,
format
* uplugin: remove engine version in source code
* module.h/cpp: remove empty .h file definition and set cpp file as
defaultmoduleimpl
* converted from actor to handle + subsystem + function library
* general cleanup of deprecated functions
* Helpers added in many places to simplify execution flow
* async task created for oauth login
* many inputs migrated to native

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Co-authored-by: 0xFirekeeper <0xFirekeeper@gmail.com>

Author: dirtycajunrice