Manager 3 - fully reworked

Updated to new Core 4 commands API - reworked all commands, subcommands and their visuals.
Extremely simplified code with the new API and use of many built-in utilities.
Stopped using server for uploading your files. (Themes: Save your theme and pull a request to upload it into Themes folder in this repo. Scripts: Pull a request to upload your script that is using Core.lib into Scripts folder in this repo.)
You can now download online configs from LiquidCloud, online scripts and themes from this repo. Alternatively you can also provide direct link to any file with the right format.
Removed deprecated MusicPlayer. (it might get reworked and added back later)