Split up framework arg when branch is included

When including a branch in the framework argument the `framework` object was including the branch resulting in an error fetching the remote files (ex. https://gist.github.com/jimmynotjim/b3305722be643af60f83#file-gistfile1-txt-L6).

### Changes

* Split out `branch` and `framework` objects when a branch is present in the passed argument
* Defaulted 'framework' object when no branch is present in the passed argument

### Testing

* Run `yo evolved wordpress#7-core-theme` and should pull from `7-core-theme` branch

   ```bash
   info ... Fetching http://github.com/evolution/wordpress/archive/7-core-theme.tar.gz ...
   ```
* Run `yo evolved wordpress` and should pull from latest release (currently v1.0.10)

   ```bash
   info ... Fetching http://github.com/evolution/wordpress/archive/v1.0.10.tar.gz ...
   ```

### Review

@ericclemmons
@EvanK