Content-Type header should be configurable

[skystrife]

We should be able to specify the Content-Type header for the responses. Relevant code: https://gist.github.com/dcollien/7301248#file-c_json_servlet-c-L157-L158

Otherwise, the server always responds with a Content-Type: "text/html; charset=ISO-8859-1", which will break utf-8 in responses.