Fixed failing test org.openehr.adl.flattener.OperationalTemplateBuilderTest#testOntologyMerge

This is a fix for the issue raised on the failing org.openehr.adl.flattener.OperationalTemplateBuilderTest#testOntologyMerge. 

Changed implementation of Map from HashMap to LinkedHashMap. 

The two different Map implementation have different performance characteristics. If write operations are important we should keep HashMap. I guess read operations are most important. And here the LinkedHashMap is faster. 

Bjørn Næss