Add collapsible section component.

Can now collapse server categories.
Client remembers collapse state, incl. advanced appearance settings.

src/redux/reducers/section_toggle.ts

@@ -0,0 +1,37 @@
+export interface SectionToggle {
+    [key: string]: boolean
+}
+
+export type SectionToggleAction =
+    | { type: undefined }
+    | {
+        type: "SECTION_TOGGLE_SET";
+        id: string;
+        state: boolean;
+      }
+    | {
+        type: "SECTION_TOGGLE_UNSET";
+        id: string;
+      }
+    | {
+          type: "RESET";
+      };
+
+export function sectionToggle(state = {} as SectionToggle, action: SectionToggleAction): SectionToggle {
+    switch (action.type) {
+        case "SECTION_TOGGLE_SET": {
+            return {
+                ...state,
+                [action.id]: action.state
+            }
+        }
+        case "SECTION_TOGGLE_UNSET": {
+            const { [action.id]: _, ...newState } = state;
+            return newState;
+        }
+        case "RESET":
+            return {};
+        default:
+            return state;
+    }
+}