Update Batch Changes landingpage screenshots

Created by: mrnugget

This changes the three screenshots of example batch specs to

• fix the order of the screenshots (the "refactoring" and "configuration" screenshots were mixed up)
• use templating in the steps to show off how powerful Batch Changes can be
• remove mentions of "campaigns"
• remove mentions of "sourcegraph-testing"
• remove wrong comments (comment in a spec said "do not replace in node modules" but the code didn't reflect that)