Refactor taggable module
Refactor taggable module

The code now uses very thin dynamically defined methods that point to more generic statically defined methods to make it easier to read. The implementations of the various getter/setter methods have also been built out in order to pass tests for the old code.

theodi/govuk_content_models,dinuksha/Test,theodi/govuk_content_models,dinuksha/Test,alphagov/govuk_content_models