Update inferred denials to credit tightness

[cfarm]

Replace all references to "inferred denials" and the den_ filename prefix to "credit tightness" and crt_.

Testing

• ./setup.sh
• gulp test should pass
• gulp watch
• visit http://localhost:5000/#section-linechartindex and confirm the Credit tightness index charts display data

Screenshots

Notes

Todos

Checklist

• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the front end playbook
• Passes all existing automated tests
• New functions include new tests
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged
• Visually tested in supported browsers and devices
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)

[hillaryj]

Works for me! Looking good.