Synthesize contextmenu Events in EventSynthesizer

Problem
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Need to know when contextmenu events happen on the hit area for an AwesomeMap.

Solution
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Listen for contextmenu events on the host element for the EventSynthesizer and dispatch when these events occur.

Unit Tests
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Covering new behaviors.

How To +10/QA
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- Travis CI should pass.

@lancefisher-wf @robbecker-wf @patkujawa-wf @georgelesica-wf @tomconnell-wf @todbachman-wf