EMFolderSelector: Make EM_FOLDER_SELECTOR_RESPONSE_NEW private.
EMFolderSelector: Seal up the public instance struct.
EMFolderSelector: Implement EAlertSink interface for real.
EMFolderSelector: Further cleanups.
EMFolderSelector: Add a "can-create" property.

Replaces the EM_FOLDER_SELECTOR_CAN_CREATE flag, and can also be set
after the selector dialog is instantiated.

This makes EMFolderSelector a little more "subclassable".
EMFolderSelector: Add a "caption" property.

Replaces the 'text' argument when creating a new dialog, and can be
changed after the dialog is created.

This makes EMFolderSelector a little more "subclassable".
EMFolderSelector: Add a "default-button-label" property.

Replaces the 'oklabel' argument when creating a new dialog, and can be
changed after the dialog is created.

This makes EMFolderSelector a little more "subclassable".
EMFolderSelector: Remove 'title' argument when creating.

Just call gtk_window_set_title() after creating the dialog.

This makes EMFolderSelector a little more "subclassable".
EMFolderSelector: Override constructed() method.

Now that all the instantiation arguments have either been eliminated or
made into GObject properties, we can initialize the dialog properly via
the constructed() method instead of some custom internal function.

This makes EMFolderSelector a LOT more "subclassable".
Add em_folder_selector_get_content_area().

A more useful alternative to gtk_dialog_get_content_area().
Add em_folder_selector_get_selected().

Will eventually replace em_folder_selector_get_selected_uri().
Add em_folder_selector_set_selected().

Mostly a convenience function so callers don't have to dig up the
dialog's folder tree widget.
EMFolderSelector: Add a "folder-selected" signal.

This makes EMFolderSelector a little more "subclassable".
EMFolderSelector: Use an ETreeViewFrame.

Convert the folder selector's "New" button to a [+] button on an inline
toolbar beneath the folder tree.  The symbolic button looks better, and
clicking it no longer triggers a "response" signal, which terminates a
gtk_dialog_run() call.  We don't want gtk_dialog_run() to terminate in
this case.
EMFolderSelector: Add an activity bar.
Add em_folder_selector_new_activity().

Returns a new EActivity configured to display status and error messages
directly in the selector dialog.
Add EMailFolderCreateDialog.

Subclass of EMFolderSelector, replaces em_folder_utils_create_folder().