Use Pagedown instead of WMD

WMD is no longer maintained (in fact it's no longer available) and Pagedown
(https://code.google.com/p/pagedown/wiki/PageDown) is its spiritual successor.

U#	new file:   forum/skins/common/media/pagedown/local/Markdown.local.fr.js
Merge branch 'pagedown'

Conflicts:
	forum/skins/default/templates/ask.html