Fix: Icons collapsing in flex.

Feature: Remember what channel was opened last.
Channels: ESC to focus message box / cancel editing.

src/redux/reducers/last_opened.ts

@@ -0,0 +1,29 @@
+export interface LastOpened {
+    [key: string]: string
+}
+
+export type LastOpenedAction =
+    | { type: undefined }
+    | {
+        type: "LAST_OPENED_SET";
+        parent: string;
+        child: string;
+      }
+    | {
+          type: "RESET";
+      };
+
+export function lastOpened(state = {} as LastOpened, action: LastOpenedAction): LastOpened {
+    switch (action.type) {
+        case "LAST_OPENED_SET": {
+            return {
+                ...state,
+                [action.parent]: action.child
+            }
+        }
+        case "RESET":
+            return {};
+        default:
+            return state;
+    }
+}