- also remember last selected melodies path

- better safe than sorry

- from melody preview so far

- appropriate button to invoke that
- use insert signal to squeeze divided parts after first fragment

- seems like adding melodies to QML model has to be called with delay

- melody wrapper got preview button
- which invokes that preview component

- perform all operations on working list of Tlevel
  instead of extra list
- simpler code, less memory

- creates melody preview only when visible on the list
- is capable of reordering by dragging or from code

Save, load melody title and composer for levels. Show them on melody preview. So melody preview improved. Also grab title text from XML "movement-title" key (only "work-title" was supported so far)