* Update i18n-helper to allow substitutions of react components and wrapping of translation substrings
* Simplify code in i18n-helper.js related to substitutions, including react substitutions.
* Remove wrapper support from i18n in favour of using translations in substitutions.
* Fix i18n-helper substitution logic: ensure correct index of substitution is applied
* Throw error if there are not enough substitutions for a translation phrase
* Adds unit tests for now i18n-helper substitution functionality
* Fix grammar, react element line spacing and test layout+readability in i18n-helper.test.js
