R1:270916a26e67

Support WOFF files in Celerity and add Source Sans Pro

Summary:
- Allow Celerity to map and serve WOFF files.
- Add Source Sans Pro, Source Sans Pro Bold, and the corresponding LICENSE.
- Add a `font-source-sans-pro` resource for the font.

Test Plan:
- Changed body `font-face` to `'Source Sans Pro'`.
- Added `require_celerity_resource('font-source-sans-pro')` in StandardPageView.

Works in Firefox/Chrome/Safari, at least:

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Reviewers: btrahan, chad

Reviewed By…