UI: Dark theme consistency for Scenes vs Sources

- Selected but unfocused Source colour
- Scenes font
- Padding when editing Source name

UI/data/themes/Dark.qss

@@ -100,12 +100,19 @@ QMenuBar::item {
     background-color: rgb(58,57,58); /* dark */
 }
 
-QListWidget::item:selected:!active {
+QListWidget {
+    font-family: "MS Shell Dlg 2";
+    font-size: 8pt;
+}
+
+QListWidget::item:selected:!active,
+SourceTree::item:selected:!active {
     color: rgb(255, 255, 255);
     background-color: rgb(48,47,48);
 }
 
-QListWidget QLineEdit {
+QListWidget QLineEdit,
+SourceTree QLineEdit {
     padding-top: 0px;
     padding-bottom: 0px;
     padding-right: 0;