Fix dropped events issue in Order-watcher and Contract-wrappers subscriptions

[fabioberger]

Description

Prior to the acceptance and implementation of EIP234 by Geth and Parity, it was not possible to fetch blocks by blockHash. This lead to the incorrect logs being returned for blocks that got uncled during a block-reorg. What made matters worse is that instead of throwing an error for a blockNumber the node didn't know about, it would return an empty set of logs, making a block without logs indistinguishable from an unknown block.

This PR updates our code to fix this issue, which should make our event watching much more robust.

Testing instructions

Types of changes

Checklist:

• Prefix PR title with [WIP] if necessary.
• Prefix PR title with bracketed package name(s) corresponding to the changed package(s). For example: [sol-cov] Fixed bug.
• Add tests to cover changes as needed.
• Update documentation as needed.
• Add new entries to the relevant CHANGELOG.jsons.

[coveralls]

Coverage increased (+0.02%) to 85.001% when pulling a05530f on upgradeBlockstream into fc33eac on development.