Create the scaffold for the new charmstore v4 api

This branch creates the scaffold for the new charmstore v4 api and injects it into the app. It also adds the `getIconPath` method and swaps the v3 version for it. At the time of writing the current jujucharms backend has issues with returning some of the icons so this branch cannot land until those fixes are made.
so this wasn't true any more. If the charm was local we could get the icon from the Juju server I had thought. @frankban added the code to juju-core to support it.