Add schema.org RDFa to bootstrap theme

We added schema.org structured data (RDFa) to the prog theme in 3.14, but then
deprecated the prog theme in favour of the bootstrap theme for 3.14. However,
bootstrap lacked the schema.org RDFa. This commit brings bootstap up to parity
with prog.

Signed-off-by: Dan Scott <dan@coffeecode.net>