QmlDesigner: Unify the look of the tab bar

Change-Id: I2778b959ad75473cbba3639e008a03a105357180
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/qmldesigner/qmldesignerextension/connectioneditor/connectioneditor.qrc

@@ -1,7 +1,6 @@
 <RCC>
     <qresource prefix="/connectionview">
         <file>stylesheet.css</file>
-        <file>panel.png</file>
         <file>panelselected.png</file>
         <file>plus.png</file>
         <file>minus.png</file>

src/plugins/qmldesigner/qmldesignerextension/connectioneditor/stylesheet.css

@@ -138,11 +138,9 @@ QTabBar::tab:selected {
     color: #3c3c3c;
 }
 
+
 QTabBar::tab {
-image: url(:/connectionview/panel.png);
+    width: 80px;
-
-    width: 130px;
-
     height: 22px;
     margin-top: 0x;
     margin-bottom: 0px;
@@ -150,6 +148,7 @@ image: url(:/connectionview/panel.png);
     margin-right: 0px;
     font: bold;
     font-size: 11px;
+    background-color: #444444;
     color: #EEEEEE;
 }
 

src/plugins/qmldesigner/qmldesignerplugin.qbs

@@ -584,7 +584,6 @@ Project {
                 "connectioneditor/dynamicpropertiesmodel.cpp",
                 "connectioneditor/dynamicpropertiesmodel.h",
                 "connectioneditor/minus.png",
-                "connectioneditor/panel.png",
                 "connectioneditor/panelselected.png",
                 "connectioneditor/plus.png",
                 "connectioneditor/stylesheet.css",