Add canvas feature to display articles
It's different from view_as_foo feature because it only manage the main panel content.
This way, we dont need to duplicate lot of code to arrange article content as we need.
Add get_articles_canvas function
Add articles_canvas input field
add canvas field to define display of article content (default is 'standard')
add canvas field to manage display of article content
add canvas directory with standard canvas (one panel for comments and one for attachments) and one_panel canvas (only one panel for comments and attachments)
delegate display of article content to canvas
fix small bug in digg rendering
Merge branch 'master' of http://github.com/cbattarel/yacs into checkcanvas
[canvas] correct undefined indexes notices and undefined variable notice