Added setting manager extensions.

src/Volo.Abp.Settings/Volo.Abp.Settings.csproj.DotSettings

@@ -0,0 +1,2 @@
+<wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:String x:Key="/Default/CodeInspection/CSharpLanguageProject/LanguageLevel/@EntryValue">CSharp71</s:String></wpf:ResourceDictionary>

src/Volo.Abp.Settings/Volo/Abp/Settings/SettingManagerExtensions.cs

@@ -17,5 +17,15 @@ namespace Volo.Abp.Settings
                 StringComparison.OrdinalIgnoreCase
             );
         }
+
+        public static async Task<T> GetAsync<T>([NotNull] this ISettingManager settingManager, [NotNull] string name, T defaultValue = default) 
+            where T : struct
+        {
+            Check.NotNull(settingManager, nameof(settingManager));
+            Check.NotNull(name, nameof(name));
+
+            var value = await settingManager.GetOrNullAsync(name);
+            return value?.To<T>() ?? defaultValue;
+        }
     }
 }

src/Volo.Abp.Settings/Volo/Abp/Settings/SettingManagerSyncExtensions.cs

@@ -19,5 +19,16 @@ namespace Volo.Abp.Settings
 
             return AsyncHelper.RunSync(settingManager.GetAllAsync);
         }
+
+        public static T Get<T>([NotNull] this ISettingManager settingManager, [NotNull] string name, T defaultValue = default)
+            where T : struct
+        {
+            return AsyncHelper.RunSync(() => settingManager.GetAsync<T>(name, defaultValue));
+        }
+
+        public static bool IsTrue([NotNull] this ISettingManager settingManager, [NotNull] string name)
+        {
+            return AsyncHelper.RunSync(() => settingManager.IsTrueAsync(name));
+        }
     }
 }