Support item creation across CLI versions, better error handling

[jodyheavener]

Closes #69

Users who use >= 2.6.2 of 1Password CLI with the extension are encountering errors when creating/saving an item.

This PR does the following:

• Updates to v0.1.7 of op-js, which now correctly handles item creation before and after v2.6.2 of the CLI, where creation logic was modified.
• Updates how we handle errors coming from the CLI. Specifically op-js now handles parsing the error response from CLI, so we don't need to.
• Handles a couple other instances where a response value from a CLI command was undefined.