add zoom in/out feature#45

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re7w12u wants to merge 4 commits intoseveves:masterfrom

Commits on Jan 12, 2018

INTROduce zoom in/out feature
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Commits on Jan 13, 2018

implement zoom in/out feature directly into service instead of relying on index.d.ts
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add comment and format fixes
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implement zoom in/out feature directly into service instead of relying on index.d.ts
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committed