Reimplement data classification to support > 64 data classes #4493
Description
The existing classification model only supports up to 64 claasifications, but alas GDPR has a taxonomy with hundreds of things in it. So we need to extend the model accordingly.
Right now, individual classifications hold a 64-bit bitmask to represent classes. We can OR classifications together by just oring the bit masks. For the new model to work, we'll need to removing this OR semantics and instead lug around sets of classifications instead.