feat(demo): add landing page with docs (#1951)

docs/app/@theme/services/tabbed.service.ts

@@ -0,0 +1,56 @@
+import { Injectable } from '@angular/core';
+
+@Injectable()
+export class NgxTabbedService {
+
+  determineTabs(tabs: any): { [tab: string]: boolean } {
+    return {
+      'overview': this.hasOverview(tabs),
+      'api': this.hasAPI(tabs),
+      'theme': this.hasTheme(tabs),
+      'examples': this.hasExample(tabs),
+    };
+  }
+
+  hasOverview(tabs: any): boolean {
+    return tabs.source.some(source => this.componentHasOverview(source));
+  }
+
+  hasExample(tabs: any): boolean {
+    return tabs.source.some(source => this.componentHasExamples(source));
+  }
+
+  hasTheme(tabs: any): boolean {
+    return tabs.source.some(source => this.componentHasTheme(source));
+  }
+
+  hasAPI(tabs: any): boolean {
+    return tabs.source.some(source => this.componentHasMethods(source) || this.componentHasProps(source));
+  }
+
+  componentHasTheme(component): boolean {
+    return component.styles &&
+      component.styles.length > 0;
+  }
+
+  componentHasProps(component): boolean {
+    return component &&
+      component.props &&
+      component.props.length > 0;
+  }
+
+  componentHasMethods(component): boolean {
+    return component &&
+      component.methods &&
+      component.methods.length > 0 &&
+      component.methods.some(method => method.shortDescription || method.description);
+  }
+
+  componentHasOverview(component): boolean {
+    return component && component.overview && component.overview.length > 0;
+  }
+
+  componentHasExamples(component): boolean {
+    return component.liveExamples && component.liveExamples.length > 0;
+  }
+}