Telemetry opt-out

[sofianhn]

• windows @alexandrudima
• mac @weinand
• linux @aeschli

Users now have the option to opt out of telemetry. To toggle telemetry open user settings and change telemetry.enableTelemetry

To test:

• Open the dev tools and set a breakpoint at application insight channel.js#79
• Do some work in the product
• make sure data flows fine by inspecting batch object.
• disable telemetry & reload the window.
• verify that only event is reported 'optout'.
• without reloading the window, enable telemetry back and verify that breakpoint is hit and data is reported.