Create a new JavaScript template file telemetry.js for telemetry services

[cvan]

For handling and injecting Sentry for JS errors (see #166) and Google Analytics for usage + perf metrics (see #168 + #170).

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Parent issue: #165
Related issues:

• submit a Request for Data Collection Review (to Mozilla Data Metrics team) #168 for submitting a Request for Data Collection Review (to Mozilla Data Metrics team)
• add default, opt-out Google Analytics script for collecting generic usage information #169 for adding GA usage data,
• collect default, opt-out basic performance timing data in Google Analytics (as custom GA events) #170 for adding GA perf data,
• Create a Sentry account for catching JavaScript errors #166 for adding Sentry for catching JS errors,
• Add a Help button (with icon and label text) and modal blurb to WebVR Template's on-page UI #167 for building the Help modal,
• Document Data Collection from telemetry services #164 for documentation/messaging