dev: improve state handling for setting screens

[justlevine]

What

This PR improves the way setting screens are saved locally and on the server.

Additionally, NPM deps have been bumped to their latest (semver-compatible) versions.

It does not affect the Providers screen.

Why

Follow up to #144

How

• The context now tracks a local/server state.
• When the state is clean, the save button is disabled.
• When the state is dirty, an indicator is shown next to the screen title and a prompt is shown to save the settings when attempting to navigate away.

Testing Instructions

Additional Info

The providers screen will be handled when the providers themselves get refactored.

Checklist:

• My code is tested to the best of my abilities.
• My code follows the WordPress Coding Standards.
• My code has proper inline documentation.
• I have added unit tests to verify the code works as intended.
• I included the relevant changes in CHANGELOG.md