cabbage-bundle-list-mode for display bundles

I found the `cabbage-list-bundle` function at the weekend, but wasn't that happy how it was displayed. 

I realized that `list-buffers` or `list-processes` display really nice table like lists, so I went a bit into the code and documentation and tried to realize something in the same manner for cabbage.

The `File` column is defined as `follow-link` and is clickable, so you get straight to the `bundle.el` file.

@senny what do you think?

![Cabbage Bundle List](http://i.imgur.com/pRMYxs9.png)
we no longer need a `let`, let's just return the result of the `mapcar` operation.