luci-base: refresh table generation

luci-base: refresh table generation

Tables are now structured with standard HTML tags:

table -> thead -> tr rows
table -> tbody -> tr rows
table -> tfoot -> tr rows

- wrap table header rows in a thead element
- wrap table body rows in a tbody element
- wrap footer rowss in a tfoot element

Footer row data can be provided by initializing any of the
form table types with .footer set to a string or function, or
overriding the renderFooterRows method.

Signed-off-by: Paul Donald <redacted>