Handling statistical security parameter

[jot2re]

Many SPDZ and SPDZ2k subprotocols require a statistical security parameter. Currently it is set statically in BasicNumericContext. However, we want to handle this in a nice way. It should instead be on the resource pool where it can be loaded either from a command line argument, or file, or as a fall-back a default value (e.g. 40 or 60).