Solving issue #3497, #3500, #3498 and #3483

For issue #3483, the old behavior is restored, i.e. the minimum width of
the ProfilePanel combobox is the maximum width of its content.

Style updated for the Exif and IPTC sub-tabs

rtdata/themes/RawTherapee.css

@@ -41,10 +41,6 @@
     padding: 2px;
 }
 
-.plainback {
-    background-color: #404040;
-}
-
 window > decoration {
   box-shadow: none;
   margin: 0px;
@@ -606,24 +602,55 @@ paned > separator {
 
 /* All tool panels have a frame except for Meta which unlike the rest is a notebook itself.
  * So we use CSS to make it look like a frame. */
-#MetaPanelNotebook.frame {
+#MetaPanelNotebook > stack > box {
     border: 1px solid #262626;
-    border-bottom-left-radius: 4px;
-    border-bottom-right-radius: 4px;
-    border-top-left-radius: 0;
-    border-top-right-radius: 0;
-    border-top-width: 0;
+    background-color: #363636;
+    border-radius: 0 0 4px 4px;
+    border-top-style: none;
+    padding: 0 3px 3px 3px;
+    margin: 0 5px 5px 5px;
 }
 
 #MetaPanelNotebook header {
     border: 1px solid #262626;
-    border-bottom-left-radius: 0;
-    border-bottom-right-radius: 0;
-    border-top-left-radius: 4px;
-    border-top-right-radius: 4px;
-    border-bottom-width: 0;
+    background-color: #363636;
+    border-radius: 4px 4px 0 0;
+    border-bottom-style: none;
     padding: 5px;
-    margin: 5px;
+    margin: 5px 5px 0 5px;
+}
+
+#MetaPanelNotebook > header > tabs {
+    background-color: #363636;
+}
+
+#MetaPanelNotebook > header tab {
+    margin: 0 5px;
+    padding: 5px;
+}
+
+#MetaPanelNotebook textview {
+    border-radius: 3px;
+}
+
+#MetaPanelNotebook entry, #MetaPanelNotebook scrolledwindow, #MetaPanelNotebook combobox {
+    margin: 2px 0 2px 0;
+}
+
+#MetaPanelNotebook entry {
+    padding: 0 1px;
+}
+
+#MetaPanelNotebook label {
+    padding: 0 5px;
+}
+
+#MetaPanelNotebook text {
+    border-color: #202020;
+    background-color: #262626;
+    border-style: solid;
+    border-width: 1px;
+    border-radius: 3px;
 }
 
 #PreviewWindow {