(core) Formula UI redesign

Summary:
Redesigning column type section to make it more user-friendly. Introducing column behavior concept.
Column can be either:
- Empty Formula Column: initial state (user can convert to Formula/Data Column)
- Data Column: non formula column with or without trigger (with option to add trigger, or convert to formula)
- Formula Column: pure formula column, with an option to convert to data column with a trigger.

Test Plan: Existing tests.

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D3092

app/client/ui2018/buttons.ts

@@ -100,6 +100,16 @@ export const bigBasicButtonLink = tbind(button, null, {link: true, large: true})
 export const primaryButtonLink = tbind(button, null, {link: true, primary: true});
 export const bigPrimaryButtonLink = tbind(button, null, {link: true, large: true, primary: true});
 
+// Button that looks like a link (have no background and no border).
+export const textButton = styled(cssButton, `
+  border: none;
+  padding: 0px;
+  background-color: inherit !important;
+  &:disabled {
+    color: ${colors.inactiveCursor};
+  }
+`);
+
 const cssButtonLink = styled('a', `
   display: inline-block;
   &, &:hover, &:focus {