Parse string of tag IDs or names to an array

+ the TagUtil module encapsulates some common tag-
  related functionality I want to be able to use in
  multiple controllers or classes.
find_tags method returns an array of Tags given a string of tag ids
Re-write the TagHandler class to have a single class method

+ Most of the functionality originally in this class is now
  found in the TagUtil module which TagHandler draws from.
Re-write NotesController#create to use TagUtil and TagHandler
method to return array of associated notes given an array of tags
method to return an associated collection of notes given a string of tag IDs
Re-write SearchController#results to use the SearchHandler class. Removes a lot of duplication.