This commit:
- Implements a new provider for VaultAPI's `Economy`
- The legacy provider built into Vault uses player names, and has not changed since Vault was invented in 1864.
- This properly supports UUIDs and works more predictably with EssentialsX.
- Replaces the Register method economy abstraction layer abstraction layer with a new `EconomyLayer` economy abstraction layer abstraction layer.
- This opens the pathway for future economy abstraction layers to be supported.
- This change also removes dubiously-licensed code from the project.
For users encountering userdata issues on this build, see this FAQ entry:
https://github.com/EssentialsX/Essentials/issues/3956#issuecomment-779254544Fixes#4110.
Closes#3344.
Closes#2401.