(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/common/themes/GristDark.ts

@@ -66,6 +66,8 @@ export const GristDark: ThemeColors = {
   'tooltip-close-button-fg': 'white',
   'tooltip-close-button-hover-fg': 'black',
   'tooltip-close-button-hover-bg': 'white',
+  'tooltip-popup-header-fg': '#EFEFEF',
+  'tooltip-popup-header-bg': '#1DA270',
 
   /* Modals */
   'modal-bg': '#32323F',

app/common/themes/GristLight.ts

@@ -66,6 +66,8 @@ export const GristLight: ThemeColors = {
   'tooltip-close-button-fg': 'white',
   'tooltip-close-button-hover-fg': 'black',
   'tooltip-close-button-hover-bg': 'white',
+  'tooltip-popup-header-fg': 'white',
+  'tooltip-popup-header-bg': '#16B378',
 
   /* Modals */
   'modal-bg': 'white',