Schema Browser Update

[RoyWilliams]

The schema is now split into core and extended attributes for the Galera objects table. The original definition is in this file. Running this as python code creates an HTML file, which can be viewed with a github trick called htmlpreview, see here.

Two differences from the oldstyle:

• The schema['fields'] dictionary has things with a name attribute but now also has things with a section attribute
• There is both schema['fields'] and schema['ext_fields']

Please change the schema browser to show these subsections to make the browser easier to read. And we have a sort of "view table" called ext_objects in the web pages, so that the extended attributes can be shown as a separate table at the bottom of the browser.