Cleanup bar line span properties

[juli27]

They used to be integers in the pre-3.0 days, where a staff or bar line could specify that it spans multiple staves. This then got simplified to a bool, but this transition wasn't done cleanly. This commit makes up for that by making sure that we only work with booleans. int values are converted appropriately when reading pre-3.0 scores.

This gets rid of all property type mismatch log messages related to span and barLineSpan.

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[cbjeukendrup]

Thanks! I thought I had already reviewed this, but apparently not. Better late than never!