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/options.h

@@ -146,6 +146,7 @@ class Options {
     bool tunnelMetaData;  // Pass through IPTC and XMP unchanged
     int histogramPosition;  // 0=disabled, 1=left pane, 2=right pane
     bool showProfileSelector;
+    bool FileBrowserToolbarSingleRow;
 
     Options ();