Use updated font-face declarations

[sareh]

Is your feature request related to a problem? Please describe.
Now that #304 is merged (as a result of investigation #285), we should update all relevant components to use the new font-face declarations.

psammead-caption
psammead-copyright
psammead-headings
psammead-paragraph
psammead-sitewide-links

Describe the solution you'd like
Update these components to import font-face declarations from psammead-styles/fonts. The snapshots should be updated to show the new names e.g. ReithSans and ReithSerif. To enable all of the fonts to be loaded into storybook, we'd need to import the relevant values from psammead-styles/fonts into .storybook/config.js

Patch release - therefore no corresponding PR required in Simorgh, as the updates should be pulled in automatically.

Describe alternatives you've considered
N/A

Testing notes
High level regression of Psammead to make sure that nothing has gone wrong.

Dev insight: Manual checking in Storybook that everything is updated, and snapshot tests should be updated (CMD + F "ReithSans" and "ReithSerif" should appear).

• Initially labelled with "Refinement needed"