New feature: search by filename and file browser toolbar optimization (issue 788)

This patch adds "Find" entry box to the toolbar to perform case-insensitive search by part of image filename.
Also, there is a new option in preferences to display File Browser toolbar as single row or not. This also solves issue with lower resolution displays.

rtgui/browserfilter.h

@@ -20,6 +20,7 @@
 #define _BROWSERFILTER_
 
 #include <exiffiltersettings.h>
+#include <glibmm.h>
 
 class BrowserFilter {
 
@@ -29,7 +30,10 @@ class BrowserFilter {
         bool showTrash;
         bool showNotTrash;
         bool showEdited[2];
-        
+
+        Glib::ustring queryString;
+        Glib::ustring queryFileName;
+
         bool exifFilterEnabled;
         ExifFilterSettings exifFilter;