Update the UI of the demo app to be the wiremock branding.

[leeturner]

This PR updates the UI of the main app to the wiremock branding rather than the mocklab branding.

• Logos updated
• CTA buttons and links now the wiremock blue
• favicon updated
• Link to the github repo now points to the wiremock url

This PR is all UI and branding. No code or dependency updates are included. These will be a separate PR.

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