feat(preview-api): emit previewAppLiveSyncError when some error is thrown while livesyncing to preview app

[Fatme]

Usage:

tns.liveSyncService.on("previewAppLiveSyncError", data => {
    console.log("LiveSync error: " + data);
});

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

No api exposed to get the errors from livesync operation

What is the new behavior?

Expose an api to get the errors from livesync operation