Add AIDirPicker and use it. Remove indra/newview/ll{dir,file}picker.{h,cpp}.

Also removed some code from the Mac/windows code in
indra/plugins/filepicker/llfilepicker.cpp that shouldn't
be in there anymore (send_agent_pause/resume and updating
the LLFrameTimer stuff).

indra/newview/llfloatervfsexplorer.cpp

@@ -5,7 +5,6 @@
 #include "lluictrlfactory.h"
 #include "llscrolllistctrl.h"
 #include "llcheckboxctrl.h"
-#include "llfilepicker.h"
 #include "llvfs.h"
 #include "lllocalinventory.h"
 #include "llviewerwindow.h"