Better workflow with adding B&B-lines

already the workflow for presets & mixer #355 #2011 is on tracker, a similar issue exists for adding new B&B to a project. Current workflow is not intuitive.
**Current workflow:**
User need to
- open B&B-editor
- click _add beat&bassline_ button
- compose
- open song-editor and find _Beat/basslineNm_ in the bottom of the project
- right-click the new BB
- Name it

**Proposed workflow:**
- open B&B-editor
- click _add beat&bassline_ button
- new popup for naming the new BB
- insert name
- compose

Both the BB in BB-editor, and the BB-track in Song-editor has now the inserted name.

All was done in one window (BB-editor).

Start by tracing the B&B-editor's “add beat&bassline” action and the current naming workflow in the Song-editor. Confirm how a new B&B and its Song-editor track are created, then verify that entering a name in the proposed popup updates both visible names.

Written by the indexing model from the issue text.