fix: set explicit referrer when changing dbkey

since for some reason HTTP_REFERER is not always set now??

tailbone/templates/themes/butterball/base.mako

@@ -747,6 +747,7 @@
                   ${h.form(url('change_db_engine'), ref='dbPickerForm')}
                   ${h.csrf_token(request)}
                   ${h.hidden('engine_type', value=master.engine_type_key)}
+                  <input type="hidden" name="referrer" :value="referrer" />
                   <b-select name="dbkey"
                             v-model="dbSelected"
                             @input="changeDB()">