Update 5.8 to consider display modes as a string instead of an Array of strings.
update example to have display be a string
Update 'display modes' to include fallback chain.
Fix display mode processing algorith.
Update the algorithm processing the manifest.
Define fallback mode and make 'browser' explicitely mandatory to implement.
tidy run
Merge pull request #173 from mounirlamouri/display_chain

Change 'display' to be a string and have a fallback chain