Add path prefix to all AJAX requests

This will handle the case where the site was deployed under a
path prefix.

static/coffee/src/calculator.coffee

@@ -20,5 +20,5 @@ class @Calculator
     $('.help').toggleClass 'shown'
 
   calculate: ->
-    $.getJSON '/calculate', { equation: $('#calculator_input').val() }, (data) ->
+    $.getWithPrefix '/calculate', { equation: $('#calculator_input').val() }, (data) ->
       $('#calculator_output').val(data.result)

static/coffee/src/courseware.coffee

@@ -1,5 +1,6 @@
 class @Courseware
   constructor: ->
+    Courseware.prefix = $("meta[name='path_prefix']").attr('content')
     new Navigation
     new Calculator
     new FeedbackForm

static/coffee/src/feedback_form.coffee

@@ -5,6 +5,6 @@ class @FeedbackForm
         subject: $('#feedback_subject').val()
         message: $('#feedback_message').val()
         url: window.location.href
-      $.post '/send_feedback', data, ->
+      $.postWithPrefix '/send_feedback', data, ->
         $('#feedback_div').html 'Feedback submitted. Thank you'
       ,'json'

static/coffee/src/main.coffee

@@ -1,3 +1,9 @@
+jQuery.postWithPrefix = (url, data, callback, type) ->
+  $.post("#{Courseware.prefix}#{url}", data, callback, type)
+
+jQuery.getWithPrefix = (url, data, callback, type) ->
+  $.get("#{Courseware.prefix}#{url}", data, callback, type)
+
 $ ->
   $.ajaxSetup
     headers : { 'X-CSRFToken': $.cookie 'csrftoken' }
@@ -18,8 +24,8 @@ $ ->
       element.schematic.update_value()
 
     schematic_value $("#schematic_#{circuit_id}").attr("value")
-    $.post "/save_circuit/#{circuit_id}", schematic: schematic_value, (data) ->
+    $.postWithPrefix "/save_circuit/#{circuit_id}", schematic: schematic_value, (data) ->
       alert('Saved') if data.results == 'success'
 
   window.postJSON = (url, data, callback) ->
-    $.post url, data, callback
+    $.postWithPrefix url, data, callback