Add developer-guide in Tuleap documentation

* Add new dev-guide section
* Add index
* Add intro
* Move Contribution wiki content into Tuleap doc
* Move GittWorkflow wiki content into Tuleap doc
* Move VirtualBox wiki content into Tuleap doc
* Move LESS wiki content into Tuleap doc
* Move LDAP wiki content into Tuleap doc
* Move Test wiki content into Tuleap doc
Add new sections from Contributor-guide:

 * Tuleap Directory Structure
 * i18n