LPS-37434 Adding new background task executor for remote staging - logic copied from StagingImpl
LPS-37434 Update backend to use the new background task executor
LPS-37434 Updating UI to fit the background remote staging
LPS-37434 The old way of reporting NO_LAYOUTS error won't work anymore due to the background task arrangement - refactoring the way we handle that error, and also cleaning up this error type, all export/import/staging processes are being transformed to background processes

Conflicts:
	portal-impl/src/com/liferay/portal/lar/backgroundtask/LayoutRemoteStagingBackgroundTaskExecutor.java