Allow puppet classes to be imported by environment

This PR allows user to import puppet classes from a specific environment manually, from both GUI and Rake. 

![screenshot1](https://f.cloud.github.com/assets/3453782/2025672/cb5ffc1c-8880-11e3-9fe1-8cf6bc45193b.jpg)

Developers can click a button to sync the classes they recently created/updated/removed in a specific environment to Foreman, without waiting for the lengthy full class/environment sync to be finished by "ruby193-rake puppet:import:puppet_classes[batch]"