Remove legacy question storage (#7)

Deletes obsolete question/answer/vote persistence and the compatibility answer endpoint. Existing databases drop the legacy tables through migration 009. Plumber replies now notify the root homeowner even when nested beneath another plumber reply. Post and reply forms prevent duplicate submissions and show progress while posting.

Reviewed-on: #7
Co-authored-by: codegirl-007 <s.raide@gmail.com>

templates/submit.html

@@ -4,7 +4,8 @@
   <h1>Ask a question</h1>
   <p class="lede">It lands on today’s hunt (Pacific time). People vote; the ranking resets at midnight PT.</p>
   {{if .Error}}<p class="banner error" role="alert">{{.Error}}</p>{{end}}
-  <form class="ask" method="post" action="/submit">
+  <form class="ask" method="post" action="/submit"
+    data-submit-once data-submitting-label="Posting…">
     <input type="hidden" name="_csrf" value="{{.CSRF}}">
     <label for="title">Title</label>
     <input id="title" name="title" type="text" required maxlength="120" value="{{.TitleVal}}" placeholder="Water heater popping after showers">
@@ -12,7 +13,7 @@
     <textarea id="body" name="body" rows="8" required maxlength="8000" placeholder="Age of the house, what you already tried, where you are in the Bay if it helps.">{{.BodyVal}}</textarea>
     <label for="city">City <span class="optional">(optional)</span></label>
     <input id="city" name="city" type="text" maxlength="80" value="{{.CityVal}}" placeholder="Oakland">
-    <button type="submit" class="btn btn-primary">Submit to today’s hunt</button>
+    <button type="submit" class="btn btn-primary" data-submit-button>Submit to today’s hunt</button>
   </form>
 </main>
 {{template "footer" .}}