Issue #310: Create 'New Pattern' dialog (dismine/valentina)

New issue 310: Create ‘New Pattern’ dialog

Susan Spencer:

When user starts Valentina and clicks on ‘New Pattern’, a dialog should appear that prompts for the file name of the pattern, measurement file, etc.

This would affect the dialog for ‘New Pattern Piece’. When the user clicks on ‘New Pattern Piece’, the dialog should prompt for information solely about the pattern piece name.

This is to improve the user experience and workflow of Valentina.