Label: Improve Project Label (Tag)

* Rename Tag to Label.
* Improve UI to edit Project Label.
    * Add scrollbar to view window and make edit window
      auto-resizable(#156).
    * Allow users to input category and name each separately(#157).
    * Show License and Language even if they have no label(#155).
    * Make the Edit button togglable.
    * Add appropriate auto-focus on the input box.
Merge pull request #219 from npcode/fix/project-label

Label: Improve Project Label (Tag)