Update to prefs.json
Mark code snippets using html

So that pygments gets language information and render
them properly.
Use titles instead of lists

Give us better headings.

Also drop the adding a distribution section, doesn't make much
sense here, we might have something like that generated from
sugar-build itself.
Add github pref
Remove bug-report bit

The commmand is not there anymore.
Add note about removing directory
Remove obsolete note
Remove official support for Fedora 18
Images for first changes in activity.info and activity.html
Add page for documenting how to contribute on these docs
Add design section in index, and start porting HIG
Remove comment on ignoring 'lib'

This is not what we are doing, is better to keep a copy of lib in each
repository.