Add new typography method in Headings component

[DenisHdz]

Resolves #343

Overall change:
Add support to allow the Headings component to use Typography Type Sizes for different scripts

Code changes:

• Allow the component to pass the script name a prop
• Add propTypes to require a script prop
• Remove previous GEL_CANON and GEL_TRAFALGAR imports
• Import new getCanon and getTrafalgar methods which make use of the new getTypeSizes() method to get the appropriate GEL Type Sizes for the component.
• Import latin.js script with the default typography GEL Types Sizes in the stories and unit test

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• I have assigned myself to this PR and the corresponding issues
• Tests added for new features
• Test engineer approval

[dr3]

Have raised #425 to improve this

[dr3]

LGTM, Great work 🎉

[DenisHdz]

Conflicts fixed 🛠

[jamesbrumpton]

LGTM. Puedes unirlo.