Ui improvements and bug fixes (#5677)

* PLT-5565 - Fixing theme colors not updating

* PLT-4721 - Removing status ind for system messages

* PLT-5735 - Fixing ellipsis in firefox

* PLT-5010 - Removing extra space in channel modal

* PLT-5584 - Inline image overrning edit textarea

* PLT-5475  - Fixing tutorials on mobile

* PLT-5142 - Disabling poitner events for status

* PLT-5728 - Fixing emoji highlight on hover

webapp/utils/constants.jsx

@@ -440,7 +440,7 @@ export const Constants = {
             linkColor: '#2f81b7',
             buttonBg: '#1dacfc',
             buttonColor: '#FFFFFF',
-            mentionHighlightBg: '#fff2bb',
+            mentionHighlightBg: '#f3e197',
             mentionHighlightLink: '#2f81b7',
             codeTheme: 'github',
             image: defaultThemeImage
@@ -465,7 +465,7 @@ export const Constants = {
             linkColor: '#2389d7',
             buttonBg: '#23A2FF',
             buttonColor: '#FFFFFF',
-            mentionHighlightBg: '#fff2bb',
+            mentionHighlightBg: '#f3e197',
             mentionHighlightLink: '#2f81b7',
             codeTheme: 'github',
             image: mattermostThemeImage