Edit Upstreams from the Admin UI

[visola]

User Story

As a user I want to quickly edit a endpoints and upstreams.

Acceptance Criteria

• On the list of listeners, there's a pencil that allow users to edit an upstream
  • When click on the pencil, a text editor with the current content opens up
  • On the editor, there's a save button that when clicked, save the changes to the original file
  • On the editor, there's a cancel button that when clicked, closes the editor without any changes to the original file
• On the top of the listeners page, there's create new upstream file button
  • When clicked, a modal asking for the file name pops up
    • if the name of the file is relative, the new file will be created in the ~/.go-proxy/upstreams directory
    • if it's a full path, then that's going to be used (requires #42)
  • After getting the file name, the editor will popup with the same characteristics as editing