Add packages required to build the library to dependencies

This allows other packages to depend on the ol3 package and get the build tools (`devDependencies` are not installed when they are transitive dependencies).  The justification here is that the ol3 package becomes useful to other packages when you are able to run the build.js task.  For this task to run all of its `dependencies` (in `package.json` terms) must be available.

Also fixes #2291.