Improve bar line Inspector and Palette

**Inspector**
- Align span combo item names with palette names
- Add a [Custom] span item: it is informative only, cannot be selected and is set by the Inspector for spans which do not match any built-in span
- Implement proper selection of span combo item when a bar line is selected in the score
- Enable/disable type combo items according to bar line type (repeats cannot be turned on/off for individual bar lines)
- Implement `spanTypeActivated()` (and renamed to `spanTypeChanged()`) to set in the score element the span selected in the Inspector
- Selecting a built-in span type updates other span values
- Added a check function enforcing correctness and consistency of span data (Span, From, To); it also set spin box mins and maxes to avoid meaningless values (like From below To and so on)
- Removed array of built-in span type data; span types are different enough to make a table useless: ad-hoc code is needed for most of them
- Removed legacy, commented-out code
- Set mins for span value spins in .ui
- A few typos here and there

**Palette**
- Labels for styles and spans made clearer (hopefully...)