Propagate locale throughout the application

[lewisbirks]

Introduce a new context/provider object for the locale which allows it to be accessed throughout the application given that the component has been wrapped in the provider.

The MultiPipelineGraph component has been updated to make use of this rather than always using en-US as the local for the date which is being displayed. By using the users locale we can render the date in the language/format preferred by that locale.

Fixes #647

Testing done

The multi-pipeline page now has the dates in the users locale, tested in English (UK) and Japanese

English (UK)

Before

After

Japanese

Before

After

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