Add dialog for File/New, update Create Pattern Piece dialog

[Susan Spencer]

When a user clicks on File/New or the New icon, a dialog should appear to prompt for pattern name, pattern type and measurement file.

The user then clicks on New Pattern Piece to start design.

Remove pattern type and measurement file dialog from Create New Pattern Piece.

Create New Pattern Piece should be disabled until new pattern file is named & created, and a measurement file selected.

This is to improve the Valentina user experience and workflow.

[Roman Telezhynskyi]

Resolved issue #282. Add dialog for File/New, update Create Pattern Piece dialog.

→ <<cset bd24040391a8>>

[Roman Telezhynskyi]

Issue #310 was marked as a duplicate of this issue.