Bug - YAML and CSV models don't allow quotes to override data type

[NeilMacMullen]

For a YAML or CSV property like p: "123" the presence of surrounding quotes should be enough to force the property to be imported as a string rather than a number.

[NeilMacMullen]

This probably means walking the object tree created by the yaml/csv deserialisers to get a bit more type information. This should be quite straightforward.