wrap input-groups in a label so they're clickable

This makes clicking an `.input-group-addon` focus the field by wrapping the `.input-group` in a `<label>`.

No `for="name"` attribute is required since the input is contained within the `<label></label>`.

However, there's no example like this in the bootstrap docs so I'm not sure if you want this or if it should just live in my template overrides.