Add workbench i18n service.
Add workbench i18n service.

Add a version of the i18n service that closely matches
what's defined in edx-platform's LMS.

lovehhf/xblock-sdk,nagyistoce/edx-xblock-sdk,jamiefolsom/xblock-sdk,Pilou81715/hackathon_edX,nagyistoce/edx-xblock-sdk,jamiefolsom/xblock-sdk,Lyla-Fischer/xblock-sdk,stvstnfrd/xblock-sdk,stvstnfrd/xblock-sdk,nagyistoce/edx-xblock-sdk,jamiefolsom/xblock-sdk,lovehhf/xblock-sdk,Lyla-Fischer/xblock-sdk,edx/xblock-sdk,nagyistoce/edx-xblock-sdk,edx/xblock-sdk,lovehhf/xblock-sdk,Pilou81715/hackathon_edX,stvstnfrd/xblock-sdk,edx/xblock-sdk,Pilou81715/hackathon_edX,lovehhf/xblock-sdk,Pilou81715/hackathon_edX,Lyla-Fischer/xblock-sdk,jamiefolsom/xblock-sdk