Support different x and y scales in the templates

Test plan: change X_RANGE to something different than Y_RANGE and regraph

Auditors: alpert
Support a url_only flag that doesn't redirect to amazon after creating a png

Test plan: $.ajax({ url: "/png?url_only=1", type: "POST", data: "js=", complete: function(data, status) { console.log(data, status); }});

Auditors: alpert