Add DialogModal and use it for close confirmations and "coming soon" features (#322)

Closes #269
Closes #196

* Add DialogModal and use it for close confirmations and "coming soon" features

* Code cleanup; add Enter key to accept emphasized dialog button

client/web/src/utilities/dialog.ts

@@ -0,0 +1,37 @@
+import { reactive, readonly } from "vue";
+
+import { TextButtonWidget } from "@/components/widgets/widgets";
+
+const state = reactive({
+	visible: false,
+	icon: "",
+	heading: "",
+	details: "",
+	buttons: [] as TextButtonWidget[],
+});
+
+export function createDialog(icon: string, heading: string, details: string, buttons: TextButtonWidget[]) {
+	state.visible = true;
+	state.icon = icon;
+	state.heading = heading;
+	state.details = details;
+	state.buttons = buttons;
+}
+
+export function dismissDialog() {
+	state.visible = false;
+}
+
+export function submitDialog() {
+	const firstEmphasizedButton = state.buttons.find((button) => button.props.emphasized && button.callback);
+	if (firstEmphasizedButton) {
+		// If statement satisfies TypeScript
+		if (firstEmphasizedButton.callback) firstEmphasizedButton.callback();
+	}
+}
+
+export function dialogIsVisible(): boolean {
+	return state.visible;
+}
+
+export default readonly(state);