Refactored into Integrate, Develop, Design + refactored the engine
Removed useless files and few unused or duplicated articles
Merge branch 'master' into design

Conflicts:
	app/helpers/DevelopPiwik.php
	app/helpers/DevelopPlugins.php
Replaced empty documents with empty sub-menus
Splitted the "MVC" guide into sub-guides
Moved a menu item
Reorganized "Develop" menu items
Fixed selected menu for Changelog and Support
The active menu item is highlighted
Merge branch 'master' into design

Conflicts:
	docs/reporting-api-segmentation.md
Changed the template
Hide the "Design" section about themes
Tweaked footer
Tweaked the quick search
Removed useless CSS
Simplified the homepage code
Introduction to the "Develop" section
Added missing API client
Improved the organization in "Integrate"
#42 Split Tracking API reference into guide + API reference