Improve screenshot capture to include all rspec hooks

Problem

We use capybara-screenshot to automatically capture a screenshot when a test/example fails. However, because it only captures a screenshot in the after hook following a failed test, it doesn't capture a screenshot if there's a failure in a before(:context) hook. It also doesn't capture the screenshot at the point of failure if the test has an after hook that uses the UI (because the screenshot is captured in a config.after hook, which is executed after the test's after hooks).

We have guidelines to work around these limits, but we can do better.

Proposal

Add our own config hooks to capture a screenshot if there's a failure at any point in a spec, including in before, before(:context), after, and after(:context) hooks.