(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.css

@@ -296,6 +296,20 @@ body {
   display: block;
 }
 
+.grist-label-required::after {
+  content: "*";
+  color: var(--primary, #16b378);
+  margin-left: 4px;
+}
+
+/**
+ * When an empty value is selected, show the placeholder in italic gray.
+ * The css is: every select that has an empty option selected, and is not active (so not open).
+ */
+.grist-form select:has(option[value='']:checked):not(:active) {
+  font-style: italic;
+  color: var(--light-gray, #bfbfbf);
+}
 
 /* Markdown reset */
 

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>