misc: save split view states

This commit simplifies the view coordinator and restructures the main view stack to not include a split view.

This removes workaround logic for single pane view support that was previously in the view coordinator.

The main view is now a stack that may contain both single and dual pane views.

The ListSelectionView further specializes DualPaneView to add an index-based or custom selection mechanism.

Gitlab: #902
Change-Id: I81c9fe579b95c8d4774c3e491a16d7600323c40c