Display platform specific table information

[marpaia]

From #29, @mike-myers-tob said:

For what it's worth, the groups table has an extended schema with Windows-only columns, and the schema page documents the extended schema columns alongside the other columns. That may confuse users of other platforms who would not see those columns in their groups table.

We need to extend genwebsitejson.py to include this data in the JSON document, and update the UI to display this information for all tables when available.

[directionless]

@zhumo this old issue seems inline with some of what you've been talking about.