Solving issue 735 : "Zooming with mouse wheel should zoom where the mouse is".

The scroll wheel is now used for scrolling the editor's tab content. If you want
to change the spin button's/slider's value or combobox entry, press the SHIFT key
while using the scroll wheel.

This patch also:
- reduce the spin buttons size (50px wide, instead of 70px)
- reduce the minimum size of the combobox (tool panels can now be narrower before
  showing the horizontal scrollbar)

Note to developers:
-------------------
When creating GUI for editor tools, please use the MyComboBox, MyComboBoxText,
MySpinButton and MyFileChooserButton derived class only in order to handle
the scroll wheel properly (-> #include <guiutils.h>).

Known bug: The MyFileChooserButton thas is a FILE_CHOOSER_ACTION_SELECT_FOLDER
does not respond correctly to the new behaviour.

rtgui/profilepanel.h

@@ -24,6 +24,7 @@
 #include <rtengine.h>
 #include <pparamschangelistener.h>
 #include <profilechangelistener.h>
+#include <guiutils.h>
 
 class ProfilePanel : public Gtk::VBox, public PParamsChangeListener {
 
@@ -33,7 +34,7 @@ class ProfilePanel : public Gtk::VBox, public PParamsChangeListener {
     Gtk::Button* load;
     Gtk::Button* copy;
     Gtk::Button* paste;
-    Gtk::ComboBoxText* profiles;
+    MyComboBoxText* profiles;
     std::vector<Glib::ustring> pparams;
     rtengine::procparams::ProcParams* custom;
     rtengine::procparams::ProcParams* lastsaved;