Technical communications/Dev wiki consolidation

This is related to User:Qgil/Contributors. The pages should probably be merged at some point, but for the moment I'm using this one for brain-dumping.

Issue

 * fragmentation of venues for contribution
 * fragmentation of documentation
 * awkward content living where it doesn't really belong

Proposed solution

 * 1 wiki for the community of end users and 3rd-party site admins
 * 1 wiki for the community of developers, bot maintainers, Labs users and engineers

Many software projects offer two venues like this; it's not unusual for the "official website" to be about documentation, support and promotion, and for the development (issue tracking, feature design and RfCs, "internal" project documentation) to happen somewhere else (like sourceforge or more recently github, or a  subdomain).

This distinction actually already appears in our own mailing lists:  is for MediaWiki users and support, and   discusses "technical organization of the Wikimedia projects (i.e.: MediaWiki development and Wikimedia operations).

Advantages and risks
Advantages:
 * 1 wiki for all things technical in the Wikimedia universe: MediaWiki development, Wikimedia operations, Bots, Labs, etc.
 * As a corollary: More integration and collaboration between members of the tech community: developers, Operations people, bot owners and maintainers, etc.
 * Also a corollary: A single entry point for all volunteers interested in joining the community.
 * No more content on mediawiki.org that's not related to MediaWiki (mostly: Wikimedia engineering project documentation)
 * Wikitech has some nifty tools like Semantic Forms that would be super useful for volunteer involvement and project documentation and replace clunky and complicated systems currently based on LST transclusion and fragile templates.
 * Through its previous merge with Labsconsole, Wikitech is now integrated with Wikimedia Labs, and therefore Gerrit. This would greatly simplify identity and credentials management for developers.

Risks:
 * Appearance of the WMF moving to their own wiki and segregating itself from volunteer developers.
 * That won't happen if the whole community of developers (paid or unpaid) agrees to make wikitech their new home.
 * Fragmentation of MediaWiki documentation: some pages are useful to both end-users and developers.
 * How many of those pages are there? Most of the documentation should already be on https://doc.wikimedia.org, and the rest can probably be split according to their audience.
 * There will be a temporary disruption as people change their habits.
 * Change brings disruption; it can't be avoided, but it can be planned carefully and minimized.

Steps

 * Discuss at length to plan everything, classify the content and determine what goes where
 * Move development-related pages to wikitech
 * Move all Wikimedia engineering content to wikitech
 * Clean up and organize the wikis, and cross-link where appropriate (like the main pages & sidebars)
 * Merge usability wiki into wikitech (p-p-p-pleaaaase)