Add more consistency to docking panels and widgets

* Dock panels shouldn't have any frame border or anything like that.
* They should have an external margin of 3 pixels at their border,
  but then no further margins on the layouts (like sub-controls for
  the pipeline state views.
* Toolbars should be Raised & Panel frames. Later we'll replace them
  with actual QToolBars to better customise the painting.

qrenderdoc/Windows/TextureViewer.ui

@@ -13,12 +13,6 @@
   <property name="windowTitle">
    <string>Texture Viewer</string>
   </property>
-  <property name="frameShape">
-   <enum>QFrame::StyledPanel</enum>
-  </property>
-  <property name="frameShadow">
-   <enum>QFrame::Raised</enum>
-  </property>
   <widget class="ToolWindowManager" name="dockarea" native="true">
    <property name="geometry">
     <rect>
@@ -1266,6 +1260,11 @@ See FAQ on &quot;Gamma display of linear data&quot;</string>
   </widget>
  </widget>
  <customwidgets>
+  <customwidget>
+   <class>RDLineEdit</class>
+   <extends>QLineEdit</extends>
+   <header>Widgets/Extended/RDLineEdit.h</header>
+  </customwidget>
   <customwidget>
    <class>ToolWindowManager</class>
    <extends>QWidget</extends>
@@ -1276,11 +1275,6 @@ See FAQ on &quot;Gamma display of linear data&quot;</string>
    <extends>QWidget</extends>
    <header>Widgets/CustomPaintWidget.h</header>
   </customwidget>
-  <customwidget>
-   <class>RDLineEdit</class>
-   <extends>QLineEdit</extends>
-   <header>Widgets/Extended/RDLineEdit.h</header>
-  </customwidget>
   <customwidget>
    <class>ThumbnailStrip</class>
    <extends>QWidget</extends>