Prevent eval time deprecations from vendor.

[rwjblue]

Since we are putting our deprecation polyfill and workflow handlers into the my-app.js, any deprecations triggered while evaluating vendor.js are still logged to the console.

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• Figure out how to move the ember-debug-handlers-polyfill to just after Ember loads
• Add config/deprecation-workflow.js to the beginning of vendor.js (via contentFor('vendor-prefix') instead of contentFor('app-prefix')).