(core) Add behavioral and coaching call popups

Summary:
Adds a new category of popups that are shown dynamically when
certain parts of the UI are first rendered, and a free coaching
call popup that's shown to users on their site home page.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3706

app/client/components/DataTables.ts

@@ -45,7 +45,7 @@ export class DataTables extends Disposable {
       cssTableList(
         /***************  List section **********/
         testId('list'),
-        docListHeader(t('RawDataTables')),
+        cssHeader(t('RawDataTables')),
         cssList(
           dom.forEach(this._tables, tableRec =>
             cssItem(
@@ -185,6 +185,10 @@ const container = styled('div', `
   position: relative;
 `);
 
+const cssHeader = styled(docListHeader, `
+  display: inline-block;
+`);
+
 const cssList = styled('div', `
   display: flex;
   flex-direction: column;