Switched to package names as app ids (#69)

* Fixes #14 (although detection is disabled in background processes due to the bug described in #60)
    * Added App icons and basic installed detection
    * Real Package Names Used as IDs + App Icons (INCONVENIENT FOR PREVIOUS VERSION USERS)
    * Switch to using extracted names (no custom names)

* Fixes #57

* Fixes #67

* Fixes #64

* Fixes #61

* Commented out APKMirror and added code to remove their Apps

* Updated README

* Switched to Flutter stable (causes some UI elements to switch back to the old material design style, but this will be fixed in later Flutter releases)

* BG task silently retries on network errors

* Updated screenshots

lib/providers/notifications_provider.dart

@@ -61,6 +61,24 @@ class ErrorCheckingUpdatesNotification extends ObtainiumNotification {
             Importance.high);
 }
 
+class AppsRemovedNotification extends ObtainiumNotification {
+  AppsRemovedNotification(List<List<String>> namedReasons)
+      : super(
+            6,
+            'Apps Removed',
+            '',
+            'APPS_REMOVED',
+            'Apps Removed',
+            'Notifies the user that one or more Apps were removed due to errors while loading them',
+            Importance.max) {
+    message = '';
+    for (var r in namedReasons) {
+      message += '${r[0]} was removed due to this error: ${r[1]}. \n';
+    }
+    message = message.trim();
+  }
+}
+
 final completeInstallationNotification = ObtainiumNotification(
     1,
     'Complete App Installation',