#79 add simplified dialog wrappers (around dir, file, etc.)

[Shula Ha-Mokshim]

add simplified dialog wrappers methods for DirDialog etc., e.g.:
DirDialog_Func()
OpenFileDialog_Func()
SaveFileDialog_Func()

Reason: Those are trivial procedures and they shouldn't take more than a single line of code to the programmer to write.

e.g.

def directory_chooser_dialog(self, dialog_title, default_value):
dialog = wx.DirDialog(None, dialog_title, default_value)
if dialog.ShowModal() == wx.ID_OK:
return dialog.GetPath()
else:
return default_value