Made bootstrap-vertical-tabs a dev dependency

According to the readme, bootstrap-vertical-tabs is only needed if you want vertical tabs, but it's included in the dependencies of the project. Unfortunately, bootstrap-vertical-tabs has a dependency on bootstrap itself, which means that the whole of bootstrap gets pulled in if you want to use angular-schema-form.

I think there are two problems with this:

1. What if you're not using bootstrap? You have to include a huge dependency that you don't want
2. What if you are using bootstrap, but you're using a non-standard version? (I'm using bootstrap-sass for example) You end up with two versions of bootstrap, potentially conflicting with each other.

I believe that anyone who still wants to use vertical tabs can manually add it as a dependency and it will still work for them.