Bug 949213 - Strings for content onboarding screen r=mbrubeck

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extra : rebase_source : 83ec63f05ec73be87fdc161833ac4f88c8c9bfcb
Bug 960144 - Toast notification image implementation r=msamuel

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extra : rebase_source : e412fda60c6a0ab964e62a209e1a732eb8e74b5e