fix: Speaker birthplace not persisted (#978)

Fixes #953: When creating or updating a Speaker, the birthplace is not persisted
when changed.

This fix ensures that birthplace, when selected, is persisted to the db.

This also updates the dropdown to allow a blank value (as birthplace is
optional).

Co-authored-by: Laura Mosher <lauramosher@users.noreply.github.com>

rails/app/controllers/dashboard/speakers_controller.rb

@@ -75,7 +75,7 @@ def speaker_params
         :photo,
         :speaker_community,
         :birthdate,
-        :birthplace,
+        :birthplace_id,
         story_ids: []
       )
     end

rails/app/views/dashboard/speakers/_form.html.erb

@@ -14,7 +14,7 @@
   <%= f.date_field :birthdate %>
 
   <%= f.label :birthplace_id %>
-  <%= f.collection_select :birthplace_id, current_community.places, :id, :name %>
+  <%= f.collection_select :birthplace_id, current_community.places, :id, :name, include_blank: true %>
 
   <%= f.label :story_ids %>
   <div class="checklist">