Move out the Plutus Ledger API definition into a seperate package

[nielstron]

Currently, the Plutus Ledger Specification in Python is baked into eopsin.
This causes two issues

1. hebi also uses the specification, which leads to code duplication
2. if pycardano wants to build things on top of the ledger specification (i.e. for deriving the ScriptContext) we would get a circular dependency

So, the Plutus Ledger definition should move to a seperate python package, that can be depended upon and re-used.

Moreover pycardano might consider moving the entire plutus data definitions out. Otherwise we will get trouble when both eopsin and pycardano explicitly depend on non-consistent versions of the ledger-spec, leading to complications (CC @cffls)

[nielstron]

An alternative to this is that pycardano decides to host the entire ledger specification, which is a viable option too.