Bug #8, Re-factor "Student Problem" post-type...

* ...So that JL-Quiz can get taxonomy data
* To be used in JuxtaLearn_Quiz_Scaffold::get_hub_tax_tool()
* https://github.com/mhawksey/wp-juxtalearn-hub/issues/8
* https://github.com/IET-OU/oer-evidence-hub-org/blob/quiz/CR1/scaffold/wp-juxtalearn-quiz/php/juxtalearn_quiz_scaffold.php#L106
Bug #7, Internationalization of Taxonomy tool in Student Problem

* ..Post-types. Plus other small I18n fixes.