Scale front page image responsively
Merge pull request #116 from crosswalk-project/front-page-image-1777

Scale front page image responsively
Add tutorial for embedding API
Link to new tutorial from embedding API tutorial page
Remove section about HexGL until permission received

Plan to use HexGL as an example of a full application loaded
using the embedding API. However, I haven't got permission yet
to do this, so remove the relevant sections until I get that
permission. This will enable me to push this branch to live
in the meantime.