(core) Required fields in forms and bug fixes

Summary:
- Adding little green asterisk at the end of field title.
- Fixing bug on columns component. Adding paragraph as a column and then selecting it was throwing error in the RightPanel
- Fixing boolean column bug in the editor
- Adding (--Choose--) placeholder for dropdowns
- Fixing columns logic: Dragging and dropping columns can unexpectedly add more columns.
- Added favicon and default page title
- Added svg to sync file for electron.

Test Plan: Updated

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D4172

static/forms/form.html

@@ -5,8 +5,8 @@
   {{#if BASE}}
   <base href="{{ BASE }}">
   {{/if}}
-  <style>
-  </style>
+  <title>{{ TITLE }}</title>
+  <link rel="icon" type="image/x-icon" href="icons/favicon.png" />
   <script src="forms/grist-form-submit.js"></script>
   <script src="forms/purify.min.js"></script>
   <script>