v0.15.0

Flipper Release: v0.15.0

Summary:
- Added build-headless yarn target for producing a headless binary
- Crash Reporter plugin added. Details [here](https://fbflipper.com/docs/crash-reporter-plugin.html).
- Bug fixes and dependency updates

- Desktop notifications for all kinds of crashes with their callstack
- Desktop notifications when an exception occurs within [Litho's error boundaries](https://fblitho.com/docs/error-boundaries)
- Ability to deeplink to the crash entry in the Logs plugin for Android. This feature is not available in iOS as the callstack doesn't get logged through Flipper's Logs plugin
- Ability to copy the stacktrace by right-clicking it
- Ability to see the list of crashes in the Notifications hub

Reviewed By: passy

Differential Revision: D13880665

fbshipit-source-id: 92a3455bb826b6fb22858e2c4c88c0b9ace91a5f