Move CI to Azure Pipelines

[daviwil]

Description of the Change

Trying out Azure DevOps Pipelines for the GitHub package!

Remaining

• Run tests on Linux, macOS, and Windows
• Publish test results
• Fail the check when the test step fails, but still publish test results
• Lint in an independent job
• Test snapshot in an independent job
• Fix the Windows build failures
• Implement a build matrix of Atom versions within each platform
• Refactor common elements out of builds
• Determine whether or not this addresses "WorkerManager when the manager process is destroyed destroys all the renderer processes..." #1688
• Move to our own, independent Azure DevOps account, so we don't clobber the queue for Electron and Atom (and vice versa)
• Set up the GitHub app on this repository for Checks goodness
• Replace build badges in the README with an Azure Pipelines badge
• Remove other build YAML configuration and scripts
• Restore Coveralls integration
• Deactivate other build integrations

[coveralls]

Coverage increased (+0.6%) to 85.528% when pulling 2bc7531 on try-vsts-ci into 26c39ee on master.

[smashwilson]

🚋 choo choo