add a plugin that gathers errors and fails the gulp task if errors were recorded

[timjroberts]

Currently the gulp-npmworkspace plugins have a continueOnError option. When that option is used, errors are output but the enclosing task will run to completion. This doesn't work so well when you're running tasks in a build environment where you will want that build to fail because of the reported errors.

Consider introducing a new plugin that allows errors to be recorded and then output at the end of a running gulp task where, by default, the plugin will throw an error if any error was encountered in the stream (regardless of any continueOnError parameters).