IDEX-1395 git output stream not display anymore while importing. Creating a new reusable client service to subscribe to import output events and display the output as notifications.

Task-Url: https://jira.codenvycorp.com/browse/IDEX-1395
IDEX-1395 git output stream not display anymore while importing. For import feature, use the new and reusable import project notification subscriber to display the import process output as notifications.

Task-Url: https://jira.codenvycorp.com/browse/IDEX-1395
IDEX-1395 git output stream not display anymore. Improving the client service, adding a subscribe method for existing already shown notification

Task-Url: https://jira.codenvycorp.com/browse/IDEX-1395