Workspace/WorkspaceView changes

This is a potential API for atom.workspace. The api's for Workspace and WorkspaceView are combined to create a single more approachable API.
These changes were made assuming we will combine EditorView/Editor and PaneView/Pane. If those are combined `WorkspaceView::eachEditorView` becomes `Workspace::eachEditor` and `WorkspaceView::getActiveView` becomes `Workspace::getActivePane().getActiveItem()`