Fix form handling for user feedback

issue was noticed on demo site, but possibly existed elsewhere?  also not 100%
sure about this fix, but it's believed to be okay...

tailbone/forms/core.py

@@ -918,16 +918,13 @@ class Form(object):
             if self.request.method != 'POST':
                 return False
 
-            # we assume data is in the form of POST params
-            controls = self.request.POST.items()
-
-            # but if not, we can try to parse request body as JSON
-            if not controls:
-                try:
+            # use POST or JSON body, whichever is present
+            # TODO: per docs, some JS libraries may not set this flag?
+            # https://docs.pylonsproject.org/projects/pyramid/en/latest/api/request.html#pyramid.request.Request.is_xhr
+            if self.request.is_xhr:
                 controls = self.request.json_body.items()
-                except ValueError:
-                    # not a valid JSON body, so no data
-                    controls = []
+            else:
+                controls = self.request.POST.items()
 
             dform = self.make_deform_form()
             try:

tailbone/static/themes/falafel/js/tailbone.feedback.js

@@ -27,8 +27,13 @@ let FeedbackForm = {
             }
 
             this.$http.post(this.action, params, {headers: headers}).then(({ data }) => {
-                this.showDialog = false
+                if (data.ok) {
                     alert("Message successfully sent.\n\nThank you for your feedback.")
+                    this.showDialog = false
+                } else {
+                    alert("Sorry!  Your message could not be sent.\n\n"
+                          + "Please try to contact the site admin some other way.")
+                }
             })
         },
     }