Refactor the project clone panel

Created by: rspeicher

• Updates the projects.js file to coffee
• Refactors the actual JS code to:
  • Remove the function, just do it automatically when the element exists.
  • Works on both a and button elements.
• Removes the various :javascript blocks that were calling the method.
• Removes some duplication in the projects/empty view and renders the clone_panel partial instead.
• Adds an empty_repo? method to Repository role and adds specs for it.
• Removes a random projects/_show partial that I couldn't find actually being used anywhere. Please correct me if I'm wrong about that one and I'll revert before you merge.