Working Soundcloud export

Adds an 'upload' property to ExportFormatSpecification, to indicate that files
exported with that format specfication should be uploaded to Soundcloud, and
makes it editable in the export format dialogue.
Adds fields for the Soundcloud username & password to the file format selection
page, as well as an option to make the uploaded files public and open them in
the system browser.

Possible improvements not yet implemented:
- make upload happen in its own thread
- cosmetic tidying up of dialogue control layout
- remember username & password

gtk2_ardour/export_dialog.h

@@ -32,6 +32,7 @@
 #include "export_file_notebook.h"
 #include "export_preset_selector.h"
 #include "ardour_dialog.h"
+#include "soundcloud_export_selector.h"
 
 #include <gtkmm.h>
 
@@ -43,7 +44,8 @@ namespace ARDOUR {
 class ExportTimespanSelector;
 class ExportChannelSelector;
 
-class ExportDialog : public ArdourDialog {
+class ExportDialog : public ArdourDialog, public PBD::ScopedConnectionList 
+{
 
   public:
 
@@ -79,6 +81,7 @@ class ExportDialog : public ArdourDialog {
 	boost::scoped_ptr<ExportTimespanSelector> timespan_selector;
 	boost::scoped_ptr<ExportChannelSelector>  channel_selector;
 	boost::scoped_ptr<ExportFileNotebook>     file_notebook;
+	boost::scoped_ptr<SoundcloudExportSelector> soundcloud_selector;
 
 	Gtk::VBox                                 warning_widget;
 	Gtk::VBox                                 progress_widget;
@@ -130,6 +133,8 @@ class ExportDialog : public ArdourDialog {
 
 	float previous_progress; // Needed for gtk bug workaround
 
+	void soundcloud_upload_progress(double total, double now, std::string title);
+
 	/* Buttons */
 
 	Gtk::Button *           cancel_button;