ScrambleDB initial draft

[jschneider-bensch]

This is a basic version of a ScrambleDB implementation to get us going.

Some improvements that should be addressed later:

• allow for DB contents other than field elements, i.e. use some kind of rerandomizable hybrid encryption scheme instead of plain Elgamal encryption,
• documentation is really lacking,
• simplify definitions of table types; there is a lot of redundancy here,
• where scalars must be sampled, perhaps move the sampling part to the callee instead of doing it here and just pass in the required number of random bytes

[franziskuskiefer]

Some improvements that should be addressed later:

Do you want to put this into an issue?