fix(config): don't persist currentConfigName if not provided

Ran into an issue where `getConfig` was returning undefined during `addScopeMethods` during bootstrapping upon subsequent login attempts, thus throwing errors. Noticed my localStorage value for `currentConfigName` was `null`, which resolved to a config key name of `"null"` which obviously didn't exist in the config hash. It should be noted that I'm not using the multiple-config functionality. Seems like persisting this key shouldn't happen unless it's explicitly registered as a custom config, anyhow. 

Hope this is the "right thing to do" ... have a hard time following coffeescript sometimes.  =]