Merge pull request #57 from box/data-providers-t2

Add data providers
Add shortcut method to extend a layout
Merge pull request #61 from box/layoutbase-extend

Add shortcut method to extend a layout
Add info about custom layout modes
Update page styles info
v0.5.0
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
v0.5.1
Fix issue with optimistic asset prefetching in non-svg browsers
Merge pull request #63 from box/non-svg-page-1-asap

Fix issue with optimistic asset prefetching in non-svg browsers
v0.5.2
LazyLader: only load visible pages initially
Merge pull request #67 from box/lazyloader-perf

LazyLader: only load visible pages initially
Fix IE9 issue with box-sizing: initial

IE9 (and maybe other versions of IE) apparently do not support
`box-sizing: initial`, and the initial (default) value must be
named explicitly as `box-sizing: content-box`.
Merge pull request #69 from box/ie9-box-sizing-override

Fix IE9 issue with box-sizing: initial
v0.5.3