Please work on a schema for saving user settings in XML.

This should be flexible enough to allow unknown settings later, without changing the schema or validation.

r67 includes initial release of XML settings codes

settings.xsd is the simple schema of the generated settings.xml file

This needs QA. I found a lot of oddities in switching this over. See my frustration post on the discussion group. Because of this, we need to do multiple file writes (no where near previous, I believe 3 vs 17) when updating the entire scope of preferences. There are also other situations where updating a settings.variable in other modules (playfield.py) requires a SettingsFileWrite() call in order to actually save the settings.

Due to the handling of XML by python's minidom, there is a certain amount of whitespace creep that occurs when outputting the xml file. As it stands now, it should only be a line break between elements and a linebreak between the start and end tags of elements.

Please run this through the gauntlet and let me know if there are any problems.