Fix source location of cf-icons fonts

[Scotchester]

Changes

• Source of font files in the Grunt copy task is now the cf-icons package

Removals

• Stop unnecessarily watching content files, since Jekyll watch handles that.

Testing

• grunt copy -v and verify that the cf-icons font files are copied from node_modules/cf-icons/src/fonts to static/fonts

Preview this PR without the whitespace changes

Screenshots

Notes

• As discussed with @jimmynotjim, these tasks need a bigger overhaul in the near future, and probably a migration to Gulp, which seems to be what we're standardizing on. This is just a couple small band-aids.

Checklist

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