add the ability to add mixins to a document
fix xml mapping and tests, add readonly to field mappings
autodetect protected properties
ommit canRemoveProperty check on insert (there is nothing to remove ...)
fix whitespace
add tests and throw exception when attempting to change ro property
removed readonly and changed ProtectedPropertyTest to fail without check in UoW
remove check for silent ignore of update of protected property
add a test for resetting documentLocales
fix handling of documentTranslations and documentLocales
Merge pull request #269 from uwej711/mixins

add the ability to add mixins to a document