Add a section for plugin extensions
Add a section for plugin extensions

The build.gradle will apply gradle srcipte from plugin extension
When install the plugin with "gradleReference" framework.
The gradle can set ext.multiarch=true to support multiple APKs by
default, so add this section in here.

CrandellWS/cordova-android-template,CrandellWS/cordova-android-template,CrandellWS/cordova-android-template