Issue #220: Rename 'Tool for union two details' to 'Union tool' (dismine/valentina)

New issue 220: Rename ‘Tool for union two details’ to ‘Union tool’ https://bitbucket.org/valentinateam/valentina/issue/220/rename-tool-for-union-two-details-to-union

Susan Spencer:

Rename ‘Tool for union two details’ should be renamed to ‘Union tool’ to clarify what it does.