UI: Adjust list style of settings sidebar

Add padding between items and border; increase inner padding a
bit; make list items rounded; add spacing between list items.

UI/data/themes/Yami.qss

@@ -222,12 +222,12 @@ SourceTree QLineEdit:focus {
 
 OBSBasicSettings QListWidget {
     border-radius: 4px;
+    padding: 3px;
 }
 
 OBSBasicSettings QListWidget::item {
-    padding-left: 4px;
-    padding-top: 5px;
-    padding-bottom: 5px;
+    border-radius: 4px;
+    padding: 6px;
 }
 
 /* Dock Widget */

UI/forms/OBSBasicSettings.ui

@@ -51,6 +51,9 @@
        <property name="currentRow">
         <number>0</number>
        </property>
+       <property name="spacing">
+        <number>1</number>
+       </property>
        <item>
         <property name="text">
          <string>Basic.Settings.General</string>