developer.plone.org redirects

This patch adds friendly redirects from old plone.org content to new developer.plone.org.

- Old developer manual

- Dexterity manuals 

Especially latter is important, because p.org information reflects 2009 state.

The redirect is done in Plone itself using collective.scriptedredirect addon: 

https://pypi.python.org/pypi/collective.scriptedredirect/

We do not want to put the redirects to frontend web server, because this stack is very complex to manage and is most likely be rewritten in any case (info by @martior )

If anyone wish to review or merge this patch during the following days I'd be grateful. Otherwise I'll be merging and deploying it myself next week.