Cache assets at the data-provider layer; load page 1 ASAP
Abort requests on viewer.destroy
Add prepare() method to allow preparing SVG element before preloading

This allows us to embed the SVG content for all pages we are about to
preload synchronously to avoid a throbbing spinner during realtime
progress.
Note about why blanket is commented out
Merge pull request #62 from box/page-1-asap

Load Page 1 ASAP