Translations:Release notes 0.18/15/en


 * Redesigned Start center
 * The Document tree (Model tab) now offers 3 options for how all documents are displayed, with the option set from the menu :
 * Only display the currently active document
 * Display all documents as it used to be up to FreeCAD 0.17
 * Expand the active document and collapse all others
 * When a task is active and requires user input, an icon showing a pencil now appears on the Tasks tab and disappears when the task is completed.
 * The 3D view now benefits from a new Navigation Cube to quickly orientate the view. It also has a small menu to set the projection to orthographic or perspective, as well as to fit the content to the view. The placement of the navigation cube can be set in and it can also be hidden.
 * Generic support for US Civil / Transportation Engineering units has been added. These units include ft, ft^2, ft^3, mph, and angles as degrees/minutes/seconds.  These units allow for expression of feet in decimal form, as opposed to US Building, which forces fractions of inches.
 * It is now possible to specify a custom background image for FreeCAD's main window using the preferences option.