Allow creation of Custom fields during Profile creation

Per http://forum.civicrm.org/index.php/topic,4593.msg20052.html#msg20052

The steps would be as follows:

• Create Profile
• Add some existing fields
• Notice that I need a field for this Profile (form) that doesn't exist yet
• Click "create new (custom field)"
• Create the field (with the option inline to put it in an existing custom field group or start a new one)
• The field would automatically be added to the profile I was working on, as I am returned there.

Along these lines we could look at having default custom field groups (which are represented as tables in the current architecture) for each top-level record type. This would potentially allow folks to bypass thinking about creating custom field "groups" if they didn't need that level of complexity in their data.