[ADF-2676] Demo shell pagination bug fix (#3174)

* Demo shell pagination bug fix

* tslint error fix

* user preferences service fix

* refactor

* refactor

* refactor

* unit tests added

* unit tests fix

* [ADF-2676] added documentation for app config onChange stream

* [ADF-2676] renamed onChange stream to onLoad stream

* [ADF-2676] fixed test

lib/core/app-config/app-config.service.spec.ts

@@ -16,7 +16,7 @@
  */
 
 import { HttpClientModule } from '@angular/common/http';
-import { inject, TestBed } from '@angular/core/testing';
+import { async, inject, TestBed } from '@angular/core/testing';
 import { AppConfigService } from './app-config.service';
 import { AppConfigModule } from './app-config.module';
 
@@ -72,6 +72,20 @@ describe('AppConfigService', () => {
         expect(appConfigService).toBeDefined();
     });
 
+    it('should stream only the selected attribute changes when using select', async(() => {
+        appConfigService.config.testProp = true;
+        appConfigService.select('testProp').subscribe((property) => {
+            expect(property).toBeTruthy();
+        });
+    }));
+
+    it('should stream the page size value when is set', async(() => {
+        appConfigService.config.testProp = true;
+        appConfigService.onLoad.subscribe((config) => {
+            expect(config.testProp).toBeTruthy();
+        });
+    }));
+
     it('should skip the optional port number', () => {
         appConfigService.config.testUrl = 'http://{hostname}{:port}';