Add local copy of magna-charta

- magna-charta (https://github.com/alphagov/magna-charta) is an archived project and relies on jquery, which we are trying to remove
- this commit introduces a local, unminified copy of the code to the gem and adds a test for it, based on the original code's test: https://github.com/alphagov/magna-charta/blob/master/test/magna-charta_test.js
- the main js file has also been tidied up due to linting requirements
- this has all been done so that we can rewrite magna-charta to not use jquery at a later date

app/assets/javascripts/govuk_publishing_components/lib/govspeak/barchart-enhancement.js

@@ -1,4 +1,4 @@
-// = require govuk_publishing_components/vendor/magna-charta.min
+// = require govuk_publishing_components/lib/govspeak/magna-charta
 
 window.GOVUK = window.GOVUK || {};