Rename icon assets & references

Closes #120

- Renames icon fonts and unicode references

This uses the same basic theory behind https://github.com/TryGhost/Ghost-UI/commit/8b25a3d07cda93f81d45e4c41add550afe03c01b which has been proven to work
Merge pull request #127 from PaulAdamDavis/emoji-icon-fix

Rename icon assets & references