White noise

• Make the simulation of white noise in Sensor more generic such that it can also be used in the cases that the transfer function is given as a user-specified function or as a table.
• In the first case, the integral over the transfer function squared is calculated using the QUADPACK qagi routine (adapted to use std::function instead of C-style function pointer).
• In the second case, the integral is calculated using the trapezoidal rule.