Removing L from ProofVerify input

[BasileiosKal]

Closes #227

Taking a stab at the approach proposed by @rolfhaenni in #227. This PR:

1. Removes L from the inputs of ProofVerify and calculates it as L=R+U
2. Adds a Deserialization group of steps in the core operations (also used for de-structuring).

Also removed the Precomputation steps in favor of the Deserialization ones (IMO what was a Precomputation step was a bit loosely defined).

Since I removed the text saying that the Precomputation steps can be cached, I added some text detailing how the output of create_generaotrs can be cached + some requirements (although we may want to extent upon them in the future).

We could potentially also remove theDefinitions from each operation, since those values are explicitly defined in the procedures.

Thanks again @rolfhaenni 🙌

[tplooker]

Multiple approvals, open 3 weeks, discussed on WG calls, merging