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

model/preference.go

@@ -17,8 +17,13 @@ const (
 	PREFERENCE_CATEGORY_ADVANCED_SETTINGS   = "advanced_settings"
 	PREFERENCE_CATEGORY_FLAGGED_POST        = "flagged_post"
 
-	PREFERENCE_CATEGORY_DISPLAY_SETTINGS = "display_settings"
-	PREFERENCE_NAME_COLLAPSE_SETTING     = "collapse_previews"
+	PREFERENCE_CATEGORY_DISPLAY_SETTINGS   = "display_settings"
+	PREFERENCE_NAME_COLLAPSE_SETTING       = "collapse_previews"
+	PREFERENCE_NAME_DISPLAY_NAME_FORMAT    = "name_format"
+	PREFERENCE_VALUE_DISPLAY_NAME_NICKNAME = "nickname_full_name"
+	PREFERENCE_VALUE_DISPLAY_NAME_FULL     = "full_name"
+	PREFERENCE_VALUE_DISPLAY_NAME_USERNAME = "username"
+	PREFERENCE_DEFAULT_DISPLAY_NAME_FORMAT = PREFERENCE_VALUE_DISPLAY_NAME_USERNAME
 
 	PREFERENCE_CATEGORY_THEME = "theme"
 	// the name for theme props is the team id
@@ -28,6 +33,10 @@ const (
 
 	PREFERENCE_CATEGORY_LAST     = "last"
 	PREFERENCE_NAME_LAST_CHANNEL = "channel"
+
+	PREFERENCE_CATEGORY_NOTIFICATIONS = "notifications"
+	PREFERENCE_NAME_EMAIL_INTERVAL    = "email_interval"
+	PREFERENCE_DEFAULT_EMAIL_INTERVAL = "30" // default to match the interval of the "immediate" setting (ie 30 seconds)
 )
 
 type Preference struct {