Deprecate EditorView::split* methods
Support a copyActiveItem param in Pane::split* methods
Add PaneView::getModel()
Rename EditorView::getPane -> ::getPaneView()
Suggest better alternative in deprecation warnings
Use the model methods in the commands
Merge pull request #3459 from atom/bo-remove-editor-view-split-methods

Deprecate EditorView::split* methods