Merge branch 'master' into 'gtk3'

Most conflicts seemed to be simple enough. There were a lot of `append_text` to
`append` conversions for `Gtk::ComboBoxText`. The `PopUpCommon` class also saw
a lot of changes with non-trivial conflict resolutions.

rtgui/wavelet.cc

@@ -21,6 +21,7 @@
 #include <cmath>
 #include "edit.h"
 #include "guiutils.h"
+#include "rtimage.h"
 
 using namespace rtengine;
 using namespace rtengine::procparams;