Changing device.platform to always report the platform as "browser".

The current implementation relies on the value returned by the web
browser's `navigator.platform`, which has many possible values, making
platform-specific checks difficult. For example, a browser platform
build viewed on an Android client might report the `device.platform`
as "Android", causing the Cordova app to execute code intended for
the Android platform.
Merge remote-tracking branch 'upstream/master'