Convert amazon urls inside crowdin strings into the local urls

[aronasorman]

Same thing we do with our normal assessment item strings, except we run it too over our django.mo file before we insert it in our language pack.

[aronasorman]

@jamalex should be writing a function in ka-lite that can be fed a string, and outputs a string with AWS urls turned into localhost urls.

[aronasorman]

This is needed for learningequality/ka-lite#3215 to have its full effect.