Add ability to prefetch and auto-prefetch offline data

src/app/components/option-picker/option-picker.component.html

@@ -11,6 +11,14 @@
     <i slot="start" class="fa" [ngClass]="isDark() ? 'fa-sun' : 'fa-moon'"></i>
     <ion-label>{{ isDark() ? 'To The Light!' : 'Go Dark...' }}</ion-label>
   </ion-item>
+  <ion-item button (click)="onSelect('prefetch_data')">
+    <i slot="start" class="fa fa-download"></i>
+    <ion-label>Prefetch Offline Data</ion-label>
+  </ion-item>
+  <ion-item button (click)="onSelect('toggle_auto_prefetch')">
+    <i slot="start" class="fa" [ngClass]="isPrefetch() ? 'fa-check-square' : 'fa-square'"></i>
+    <ion-label>Auto-Prefetch</ion-label>
+  </ion-item>
   <ion-item button (click)="onSelect('logout')">
     <i slot="start" class="fa fa-sign-out-alt"></i>
     <ion-label>Logout</ion-label>

src/app/components/option-picker/option-picker.component.ts

@@ -2,7 +2,7 @@ import {Component, Input, OnInit} from '@angular/core';
 import {Router} from '@angular/router';
 import {ApiService} from '../../service/api.service';
 import {PopoverController} from '@ionic/angular';
-import {DatabaseService} from "../../service/db/database.service";
+import {DatabaseService} from '../../service/db/database.service';
 
 @Component({
   selector: 'app-option-picker',
@@ -13,6 +13,9 @@ export class OptionPickerComponent implements OnInit {
   @Input() toggleDark: () => void;
   @Input() isDark: () => boolean;
   @Input() showSearch: () => void | Promise<void>;
+  @Input() isPrefetch: () => boolean;
+  @Input() togglePrefetch: () => void;
+  @Input() doPrefetch: () => any;
 
   constructor(
       protected api: ApiService,
@@ -34,6 +37,11 @@ export class OptionPickerComponent implements OnInit {
     } else if ( key === 'search_everywhere' ) {
       this.showSearch();
       this.popover.dismiss();
+    } else if ( key === 'toggle_auto_prefetch' ) {
+      this.togglePrefetch();
+    } else if ( key === 'prefetch_data' ) {
+      this.popover.dismiss();
+      this.doPrefetch();
     }
   }
 }