Feat 60: Add index page and search /subjects UI

[helen-m-lin]

closes #60

• Added home page index.html to be loaded at http://aind-metadata-service/
  • Uses Jinja2Template to render with provided context for service (name, description, version) and enabled endpoints (endpoint, description, parameters)
• User can query subjects endpoint by providing a subject_id and clicking the "Search" button.
  • Query status (including when pending) and response are displayed below. The response is first parsed for status, message, and data.
  • The raw response json can also optionally be viewed by clicking the "View raw response" button

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