Remove all default css and make Raleigh a pure fallback theme

Remove all default css and make Raleigh a pure fallback theme

It was problematic to maintain Raleigh going forward, as any
changes in it affected all themes. Also, its more robust if
each theme is a full standalone css rather than relying on
an inherited css base.

So, this changes Raleigh to a standalone theme that we can tweak
without accidentally breaking other themes, and makes the
default theme empty. In fact, we don't even add the default
provider anymore as its always empty.