Add button to remove all datasync settings from DB

seems useful for someone testing, as prep to make the switch

tailbone/templates/datasync/configure.mako

@@ -50,9 +50,57 @@
         </b-button>
         ${h.end_form()}
       </div>
+      <div class="level-item">
+        <b-button type="is-danger"
+                  @click="purgeSettingsInit()"
+                  icon-pack="fas"
+                  icon-left="trash">
+          Remove All Settings
+        </b-button>
+      </div>
     </div>
   </div>
 
+  <b-modal has-modal-card
+           :active.sync="purgeSettingsShowDialog">
+    <div class="modal-card">
+
+      <header class="modal-card-head">
+        <p class="modal-card-title">Remove All Settings</p>
+      </header>
+
+      <section class="modal-card-body">
+        <p class="block">
+          If you like we can remove all DataSync settings from the DB.
+        </p>
+        <p class="block">
+          Note that this tool normally removes all settings first,
+          every time you click "Save Settings".&nbsp; Here though you
+          can "just remove" and <span class="is-italic">not</span>
+          save the current settings.
+        </p>
+      </section>
+
+      <footer class="modal-card-foot">
+        <b-button @click="purgeSettingsShowDialog = false">
+          Cancel
+        </b-button>
+        ${h.form(request.current_route_url())}
+        ${h.csrf_token(request)}
+        ${h.hidden('purge_settings', 'true')}
+        <b-button type="is-danger"
+                  native-type="submit"
+                  :disabled="purgingSettings"
+                  icon-pack="fas"
+                  icon-left="trash"
+                  @click="purgingSettings = true">
+          {{ purgingSettings ? "Working, please wait..." : "Remove All Settings" }}
+        </b-button>
+        ${h.end_form()}
+      </footer>
+    </div>
+  </b-modal>
+
   <b-notification type="is-warning"
                   :active.sync="showConfigFilesNote">
     ## TODO: should link to some ratman page here, yes?
@@ -448,6 +496,9 @@
 
     ThisPageData.restartCommand = ${json.dumps(restart_command)|n}
 
+    ThisPageData.purgeSettingsShowDialog = false
+    ThisPageData.purgingSettings = false
+
     ThisPageData.settingsNeedSaved = false
     ThisPageData.undoChanges = false
     ThisPageData.savingSettings = false
@@ -692,6 +743,10 @@
         }
     }
 
+    ThisPage.methods.purgeSettingsInit = function() {
+        this.purgeSettingsShowDialog = true
+    }
+
     ThisPage.methods.saveSettings = function() {
         this.savingSettings = true
         let url = ${json.dumps(request.current_route_url())|n}