Respected 'inheritanceType' at Entity level

It was (incorrectly) fetched from Table-level.
http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/annotations-reference.html#annref-inheritancetype
Exclude exporting inheritanceType for INHERITANCE_TYPE_NONE
Merge pull request #897 from holtkamp/patch-3

Respected 'inheritanceType' at Entity level