qml: add "new (blank) profile" button to the tool bar editor dialog

Based on !5883 (merged). See the last three commits.

This dialog already has a "new profile" button, but it works by cloning the selected profile.

With this patch, "new profile" creates a blank profile (mid-button), and cloning functionality is retained in a different "clone profile" button (leftmost-button).

Request review @chub.