Add graphite-editor library skeleton (#34)

packages/graphite-editor/src/layout/mod.rs

@@ -0,0 +1,34 @@
+use crate::EditorError;
+type PanelId = usize;
+
+struct LayoutRoot {
+	hovered_panel: PanelId,
+	root: PanelGroup,
+}
+
+impl LayoutRoot {
+	// add panel / panel group
+	// delete panel / panel group
+	// move panel / panel group
+	// get_serialized_layout()
+}
+
+struct PanelGroup {
+	contents: Vec<Contents>,
+	layout_direction: LayoutDirection,
+}
+
+enum Contents {
+	PanelArea(PanelArea),
+	Group(PanelGroup),
+}
+
+struct PanelArea {
+	panels: Vec<PanelId>,
+	active: PanelId,
+}
+
+enum LayoutDirection {
+	Horizontal,
+	Vertical,
+}