Change getProperty -> prefs.get* within CordovaActivity
Convert usages of Config.* to use the non-static versions
Provide CordovaPlugin with CordovaPreferences. Add new Plugin.initialize()

This adds CordovaPlugin.initialize() (no args) and deprecates
CordovaPlugin.initialize(app, webView). This will allow us to refactor
more easily by using the package-private privateInitialize() to set
fields.