integrate portal webview to the default app

Based on the UX review feedback, we plan to implement portal webview
function inside the carrier default app instead of reusing the existing
portal app. This will give us more flexibility and control, also will
improve UX flow by getting rid of the some unwanted dialogues.

Test: Manual
Bug: 36002256
Change-Id: I2627d5a43039ce433006c058bb4f2c1a39113e59