configure am/pm time-format as user preference (#2789)

src/Entity/User.php

@@ -430,6 +430,20 @@ class User implements UserInterface, EquatableInterface, \Serializable
         return null;
     }
 
+    public function getTimeFormat(): string
+    {
+        if ($this->is24Hour()) {
+            return 'H:i';
+        }
+
+        return 'h:i A';
+    }
+
+    public function is24Hour(): bool
+    {
+        return (bool) $this->getPreferenceValue(UserPreference::HOUR_24, true);
+    }
+
     public function getLocale(): string
     {
         return $this->getPreferenceValue(UserPreference::LOCALE, User::DEFAULT_LANGUAGE);

src/Entity/UserPreference.php

@@ -30,6 +30,7 @@ class UserPreference
     public const INTERNAL_RATE = 'internal_rate';
     public const SKIN = 'skin';
     public const LOCALE = 'language';
+    public const HOUR_24 = 'hours_24';
     public const TIMEZONE = 'timezone';
     public const FIRST_WEEKDAY = 'first_weekday';