Only cache pixmaps for docked icons

There is little point caching a pixmap for an app that isn't in the
dock. This patch creates a function wAppIconSave that saves only if the
app icon is docked, and adds calls to that function in all the places
where an appicon can transition from undocked to docked.

It also "adds" a function wApplicationSaveIconPathFor that saves an icon
path to the configuration plist; the function already existed, it was
just static before.

Signed-off-by: Brad Jorsch <anomie@users.sourceforge.net>

src/application.h

@@ -58,6 +58,8 @@ WApplication *wApplicationOf(Window window);
 
 void wApplicationExtractDirPackIcon(WScreen *scr,char *path, char *wm_instance,
                                     char *wm_class);
+void wApplicationSaveIconPathFor(char *iconPath, char *wm_instance,
+		char *wm_class);
 
 void wAppBounce(WApplication *);
 void wAppBounceWhileUrgent(WApplication *);