role "marquee" for event carousel

http://www.w3.org/TR/wai-aria/roles#marquee
add aria roles "alert" and "status" to alerts

http://www.w3.org/TR/wai-aria/roles#alert
http://www.w3.org/TR/wai-aria/roles#status
add aria-controls to showhide_buttons

http://www.w3.org/TR/wai-aria/states_and_properties#aria-controls
add aria landmark roles
add role "checkbox" to watch buttons

http://www.w3.org/TR/wai-aria/roles#checkbox
replace noscript by modernizr's only-no-js

noscript is not rendered reliably, I am also not sure if it is valid in
XHTML.
aria role for disabled tagcloud items
Revert "add role "checkbox" to watch buttons"

This reverts commit 611445d81768d5b49e129d34c19a75e94234452d.

We were not sure if this is an improvement because checkboxes typically
do not change their labels on state change. So we decided to leave this
for now.
Merge pull request #880 from xi/feature-492-some-aria

some WAI-ARIA improvements