Use hash for storing classes in index

[noha]

Right now we use a 64 byte index key for storing behavior descriptions in the behavior registry. This limits the maximum length of the class name and at the same time wastes a lot of index key space.
To improve the situation class names should be hashed to be used as a key. That would reduce it from 64 bytes to 32 bytes in case of SHA256. The number of classes is not really high (< millions) so we could even use MD5 and reducing the key to 16 bytes instead.