Rewrite integration tests for user-sidebar component to use page objects

[dm0n3y]

Falls under umbrella issue #697.

Resources

• What's a page object? [1,2]
• Quickstart guide
• See tests/pages/components/donations/create-donation.js and tests/integration/components/donations/create-donation-test.js for in-house examples of, respectively, a page object and the page object being utilized in an integration test.
• To generate a page object, run ember generate page-object component/<component-name> in the project directory.