增加各插件图标

src/appdata/plugin/all-app-data-provider.cpp

@@ -54,7 +54,7 @@ QString AllAppDataProvider::name()
 
 QString AllAppDataProvider::icon()
 {
-    return "image://appicon/text-plain";
+    return "image://appicon/view-grid-symbolic";
 }
 
 QString AllAppDataProvider::title()

src/appdata/plugin/app-category-plugin.cpp

@@ -79,7 +79,7 @@ QString AppCategoryPlugin::name()
 
 QString AppCategoryPlugin::icon()
 {
-    return "image://appicon/text-plain";
+    return "image://appicon/applications-utilities-symbolic";
 }
 
 QString AppCategoryPlugin::title()

src/appdata/plugin/app-letter-sort-plugin.cpp

@@ -48,7 +48,7 @@ QString AppLetterSortPlugin::name()
 
 QString AppLetterSortPlugin::icon()
 {
-    return "image://appicon/text-plain";
+    return "image://appicon/ukui-capslock-symbolic";
 }
 
 QString AppLetterSortPlugin::title()