refactor(assets): assets

 * created `assets/` folder
 * moved `./app/AppInspector/resources/psd/` to `assets/psd/`
 * moved `./free-all-purpose-icons-gcons/` to `assets/free-all-purpose-icons-gcons/`

Moving `app/AppInspector/resources/psd/` to `assets/` to make final packaged app file size smaller as everything in `app/AppInspector/resources/` is copied over during `sencha app build`.