PLT-3647 Email Batching (#3718)

* PLT-3647 Added config settings for email batching

* PLT-3647 Refactored generation of email notification

* PLT-3647 Added serverside code for email batching

* PLT-3647 Updated settings UI to enable email batching

* PLT-3647 Removed debug code

* PLT-3647 Fixed 0-padding of minutes in batched notification

* PLT-3647 Updated clientside UI for when email batching is disabled

* Go fmt

* PLT-3647 Changed email batching to be disabled by default

* Updated batched email message

* Added email batching toggle to system console

* Changed Email Notifications > Immediate setting to a 30 second batch interval

* Go fmt

* Fixed link to Mattermost icon in batched email notification

* Updated users to use 30 second email batching by default

* Fully disabled email batching when clustering is enabled

* Fixed email batching setting in the system console

* Fixed casing of 'Send Email notifications' -> 'Send email notifications'

* Updating UI Improvements for email batching (#3736)

* Updated text for notification settings and SiteURL.

* Prevented enabling email batching when SiteURL isn't set in the system console

* Re-added a couple debug messages

* Added warning text when clustering is enabled

webapp/components/admin_console/webserver_mode_dropdown_setting.jsx

@@ -15,13 +15,13 @@ const WEBSERVER_MODE_HELP_TEXT = (
         >
             <tbody>
                 <tr>
-                    <td className='help-text'>
+                    <td>
                         <FormattedMessage
                             id='admin.webserverModeGzip'
                             defaultMessage='gzip'
                         />
                     </td>
-                    <td className='help-text'>
+                    <td>
                         <FormattedMessage
                             id='admin.webserverModeGzipDescription'
                             defaultMessage='The Mattermost server will serve static files compressed with gzip.'
@@ -29,13 +29,13 @@ const WEBSERVER_MODE_HELP_TEXT = (
                     </td>
                 </tr>
                 <tr>
-                    <td className='help-text'>
+                    <td>
                         <FormattedMessage
                             id='admin.webserverModeUncompressed'
                             defaultMessage='Uncompressed'
                         />
                     </td>
-                    <td className='help-text'>
+                    <td>
                         <FormattedMessage
                             id='admin.webserverModeUncompressedDescription'
                             defaultMessage='The Mattermost server will serve static files uncompressed.'
@@ -43,13 +43,13 @@ const WEBSERVER_MODE_HELP_TEXT = (
                     </td>
                 </tr>
                 <tr>
-                    <td className='help-text'>
+                    <td>
                         <FormattedMessage
                             id='admin.webserverModeDisabled'
                             defaultMessage='Disabled'
                         />
                     </td>
-                    <td className='help-text'>
+                    <td>
                         <FormattedMessage
                             id='admin.webserverModeDisabledDescription'
                             defaultMessage='The Mattermost server will not serve static files.'