expose accept and reject instead of done

some toolkit dialogs reimplement accept and reject and bypass this logic
on done. It's simpler to force the user to go through explicit accept
and reject.
add a new file dialog which uses ToolkitDialog

this unifies the api of the file dialog with that of the color dialog
and any future dialogs built from ToolkitDialog
wip commit for Qt FileDialogEx
add a default title method for toolkit dialogs
supply an appropriate default title.
minor code cleanup
finalize the FileDialogEx widget
expose FileDialogEx to the api files