Verify that mapping of boolean values works across *SV-based mappers

[fontanka16]

I had to add this into the TestableFileMapper, in order to make the mapping of booleans work for that. We should make sure it works for the others as well.

For each mapper:

Create a test (or add to existing) for the the following scenarios:

• Boolean property mapped from the value property in the map
• Boolean property mapped from the source data