Provide template tag for query-strings

[tim-mccurrach]

It is a common use case to have something like this in templates:
{% if request.token %}{{JWT_QUERYSTRING_ARG}}?={{request.token.jwt}}{% endif %}

This requires importing JWT_QUERYSTRING_ARG in the view layer and adding it to the context, and could be better achieved with a template tag {% request_token_querystring %}.