Fixes #142: added simple validation in EntityMetadata + unit test
Updated MetadataParser to call validate after creating new EntityMetadata
Moved calling em.validate() into EntityMetadata constructor
Made EntityMetadata final
Revert "Made EntityMetadata final"

This reverts commit 0b0eca06e7969e1381df513924a9ce28962df31a.
Merge pull request #154 from jewzaam/pr-validate-use-of-enum

Added validation of enums