Miscellaneous notice cleanups, flexible.incfixes, an aborted attempt at doing preview that needs more thought.

by douggreen: re-added missing callback property to the validate function. Might actually not be necessary...we'll see.

Initial port of panels mini; still need to work on the "context" ajax stuff and convert it to the new system, but the other stuff appears to work at least a little. Also include some fixes to layouts as "id" turns out to be illegal due to Drupal setting its own id string.

Templatize all panel layouts; give each layout its own directory for cleanliness. Slight improvement to the API needed for the move to work.

Initial D6 work -- this includes only panels.module stuff. Right now the drag & drop display editor works, layout, layout settings and render works. Special features such as cache and styles may or may not work.

Apply some default margin to the content areas using nested divs so that they don't splat into each other by default. Some very simple CSS can adjust/remove the padding.