Position of xsi:type attribute in ModelInfo matters

[brynrhodes]

For some reason I don't understand, the position of the xsi:type attribute in the XML ModelInfo matters:

https://github.com/cqframework/clinical_quality_language/commit/e0fd90ddcd4bf47b0218eddfeb54af9aa9e026e9

Fixup the ModelInfo serialization to produce XML that ensures that the type attribute is the first attribute listed in the ModelInfo.