Allow all TreeComponentState properties to be optional

None of these properties are guaranteed to be set on existing usages of
setState.

src/components/tree/tree.tsx

@@ -68,12 +68,12 @@ export interface TreeComponentStateProps {
 }
 
 export interface TreeComponentState {
-  hoveredNode: {
+  hoveredNode?: {
     node: PhyloNode
     isBranch: boolean
   } | null
-  tree: PhyloTreeType | null
-  treeToo: PhyloTreeType | null
+  tree?: PhyloTreeType | null
+  treeToo?: PhyloTreeType | null
   geneSortFn?: (a: number, b: number) => number | (() => 0)
 }