TPAC: Google Books preview loader

Refinements should include checking more than just the first ISBN for
embeddability and passing more identifiers to the preview loader.
Roughly equivalent to what JSPAC had though.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>
TPAC: Make Google Books Preview depend on Dojo

It would be possible, but painful, to do all of this in raw JavaScript,
so make the preview functionality depend on Dojo. Also, split out the
relevant JavaScript into its own file. Also, don't search for a preview
if no ISBNs have been gathered; I'm sure Google is never going to return
a result for ISBN:undefined.

You can test this functionality in the sample record set using ISBN
4431287752.

Thanks to Ben Shum for the review comments!

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>