REACH-93 Create new Home workspace in nwk

As in Dynamo there were added `New` button for clearing Home workspace and clearing instead of deleting the tab.
Before it a user gets a suggestion to save his workspace. And only after that the workspace is cleared. For not duplicating of tracking unsaved changes in Flood we ask Dynamo about them.

The suggestion mechanism to save changes is used only in NWK because in web browser there are possible cases when we can't find out whether a user has a corresponding file with the last changes or not (for example a user refuses to save a received file but Dynamo "thinks" it hasn't unsaved changes anymore).
@marimano,  This is another case where we can't introduce UI behaviors into the model layer.  You'll need to move this to an appropriate `View`.