Symlinks for nested dependencies

In our company, we’re going to use Bower as a generic package manager for our projects because of its flexibility and great Git integration.

It means that we will use it for back-end projects too so it’s vital for us to have all dependencies installed correctly (including dependencies of dependencies). I’ve read discussion at https://github.com/bower/bower/issues/157 and implemented symlinking of nested dependencies on `install` and `update`.

All symlinks are relative so the main project can be easily packed for further deployment. And symlinks are removed  when user uninstalls dependency.