Issue #331: Add Grainline tool to Layout mode (dismine/valentina)

New issue 331: Add Grainline tool to Layout mode https://bitbucket.org/valentinateam/valentina/issues/331/add-grainline-tool-to-layout-mode

Susan Spencer:

Create tool too add a Grainline to patternpieces in Layout mode.

This is essential information for cutting out fabric correctly.