remove every instanceOf on any @Entity object

[julien-louis]

Instanceof doesn't always work with Hibernate proxies, but sometimes it does.

As a precaution I recommend to use getType() instead when it's implemented like in Datasets & DatasetAcquisition, or use Hibernate.getClass() which return the real class, proxy or not.

We should do that with every instanceof to any @entity in the code.

ie :
if (dataset instanceof MrDataset)
should be
if(DatasetType.Mr.equals(dataset.getType()))
or
Hibernate.getClass(ds).equals(MrDataset.class)