Rationale: in practice, a ProofId was always a slot id, and
an EndId was always a request id. Now that the definitons
of SlotId and RequestId are separated from the Marketplace,
we can import and use them.
1. Replace all instances of `now()` with `await currentTime()` to get a more accurate representation of time from the block timestamp. Update examples.js to be async.
2. Move `RequestState` to `marketplace.js`
3. Delete `TestStorage` as `slashAmount` function no longer needed.
Allow proof ending to be extending once a contract is started, so that all filled slots share an ending time that is equal to the contract end time. Added tests.
Add a mapping for proof id to endId so that proof expectations can be extended for all proofs that share a given endId.
Add function modifiers that require the request state to allow proofs, with accompanying tests.
General clean up of each function’s request state context, with accompanying tests.
General clean up of all tests, including state change “wait” functions and normalising the time advancement functions.
Once a proof is marked as missing, if that missing proof is enough to slash a host, first slash the host, then check the hosts balance. If the balance has dropped below the minimum allowable collateral threshold, then remove them from the slot.
Update `Marketplace.state` getter to to take `isCancelled` into account. This state can then be used internally and externally.
Add checks to `proofEnd`, `isProofRequired`, `willProofBeRequired`, and `getChallenge` that understands if the request is in a state to accept proofs. If not, return other values.
Add `slotMustAcceptProofs` modifier, originally introduced in a later PR, which requires the request to be in state of the request accepting proofs.
Add tests for all the above.
Add a requestId mapping to the Slot type. This allows the requestId to be obtained for a slot and the StorageRequest can be looked up from the id.
Add `isSlotCancelled` to check if the request that a slot belongs to has been cancelled (not enough slots filled before expiry).
Mark Spanbroek
Eric Mastro