Issue #286: Add 'Mode' menu picklist to top menu, create enable/disable for design workflow (dismine/valentina)

New issue 286: Add ‘Mode’ menu picklist to top menu, create enable/disable for design workflow https://bitbucket.org/valentinateam/valentina/issue/286/add-mode-menu-picklist-to-top-menu-create

Susan Spencer:

Add ‘Mode’ picklist to top menu between Pattern Piece and Measurements.

Under ‘Mode’ title, list ‘Draw’, ‘Detail’, ‘Layout’

When a new pattern design is created, or a pattern design is opened, Draw becomes enabled.

When a design’s pattern piece or detail exists, Detail becomes enabled.

When a design’s detail or layout exists, Layout becomes enabled.

When a design’s layout exists, File/Export becomes enabled.

This is to improve Valentina’s user experience and workflow.