Modified instrumentation

[Kukovec]

closes #81
This PR changes instrumentation, to the format discussed during our recent meeting. A detailed explanation of the format can be found inside instrument.ts.
To this end, it makes the following changes:

• Instrumentation now constructs Init from oldFields, and Next from a conjunction of state-variable updates from fields and transition constraints from method and methodArgs.
• Instrumentation adds Gen(1) initializations (in either Init or Next) to all variables declared in the monitor, but absent from the transaction data (in oldFields or fields, respectively). This allows us to avoid Apalache errors on transactions in which data storage changes.
• Tests with expecetd instrumentation syntax have been updated to reflect the changes. No semantic changes have been made in those tests
• New tests covering the newly-supported initialization paradigm have been added
• entry-timelock.json has been fixed to comply with the transition requirements of Claim (last_error' = "contract is not initialized" whenever ~is_initialized)

[thpani]

Looks great!

I'm a bit scared about the empty conjunction (see my comment below) if the code evolves.

[Kukovec]

@thpani just fyi, it seems like the prettier reverted some of your method argument parenthesis suggestions, it's not me manually reverting these