Fix Ionic requests(white screen)

[alexandergoncharov-zz]

Issue: Ionic app should call all file URL requests with setServerBasePath method otherwise app shows just white screen.

Solution: Replaced calling setServerBasePath method to using it with all URL request.

Related issue: #486

[yuri-kulikov]

Looks good to me!

[rdss-jpupeter]

Hi all,
since this merge the plugin doen´t work for ionic 3 anymore.
actual behaviour:

1. setServerBasePath is called for the new CodePush-Update URL
2. setServerBasePath is called for the ionic default URL

--> on every App Start the default App is displayed and the user never sees the updated version.

With the #483 PR all ionic Webview 2+ issues were solved, but for me now the plugin doesn´t work anymore.

Ionic webview version:
cordova-plugin-ionic-webview 2.3.1

Ionic info