Upgrade to WKWebview

[longzheng]

https://ionicframework.com/docs/wkwebview/

Hopefully improves performance and fix some weird layout/rendering issues

• [x] Upgrade WKWebView https://github.com/ionic-team/cordova-plugin-ionic-webview#installation-instructions
• [x] Change http calls to Ionic Native HTTP https://ionicframework.com/docs/native/http/

[longzheng]

Running into issue with cordova-plugin-advanced-http plugin not storing/sending cookies set on the response with a redirect. https://github.com/silkimen/cordova-plugin-advanced-http/issues/148

[longzheng]

• [x] Change all $http calls from reject to catch

[longzheng]

• [x] After long idle, refreshing/top up no longer works

[longzheng]

Ah turns out it's due to 302 redirect on a GET call (redirect to error page) which is currently not handled (only on POST).