implemented & tested proper file attributes validation

Closes #58

Further additions/modifications to file attributes validation should be opened as a separate issue.

More than one attributes class can now be applied to a mimeType.  The map for which classes apply to which mimeTypes is defined in the property `ayamel.resource.file_attribute_validation_map` in `src/Ayamel/ResourceBundle/Resources/config/config.yml`

Extraneous file attributes will cause validation to fail, otherwise that data would end up persisting to the database.  This is slightly different from the behavior in the rest of the API where bad input is filtered out early on and just ignored.