Tweak Google Book Preview Display

Tweak Google Book Preview Display

This commit makes three changes to the Google Book preview link:

1) Move the button to the same spot on the page as the viewer.
This clarifies the relationship between the button and the viewer,
and makes it far less likely that the viewer will load off the
screen.

2) Make the button a toggle for turning the viewer on and off.

3) In conjunction with (2), add some additional text to the button
link to follow the toggling action.

Signed-off-by: Dan Wells <dbw2@calvin.edu>