Add model for ghost locations

[jcp19]

The goal of this PR is to bring down the TCB of our resource algebra formalization to what I believe is the smallest possible TCB that we can have given the absence of existentially quantified permissions in Gobra.

Our assumptions are all listed in file docs.gobra, and only have to do with the introduction and elimination of existential quantifiers.

There are a couple of todos here:

• (maybe) clean up the code and use the implementations for MonoSet and MonoMap instead of the bespoke cooliomapio and cooliosetio :)
• Make GlobalMem() an invariant established during initialization and replace the inhale/exhale pairs with code to open the invariant. Done in Add body to all functions that inhaled the invariant #35, but it depends on atomic methods and invariants gobra#983.
• Prove the last outstanding assumption: the product of all currently allocated elements for a reference is valid (might do this in a separate PR) ([WIP] Verify global validity of ghost locations #36)

PS: I introduced a new packet rather than changing package resalgebra, as the API for RAs changed slightly. I might deprecate resalgebra soon though