[orion-based] [WIP] Commands Implementation

[kevzhao2]

This PR aims to implement TShock's command subsystem, as roughly laid out in #1677. This is currently a work-in-progress; I will provide a write-up once I think it's done.

[maka-albarn[bot]]

Thanks for the pull request! TShock's maintainers would like you to go ahead and give yourself credit by updating the CHANGELOG.md as soon as you can. Your pull request will likely not be accepted without this. This both helps us document changes to TShock, as well as give you credit for your work. You deserve it, so go take credit! :sparkles: