Shaper class, with white noise

• Add Shaper class
• Shaper object stores a transfer function (bipolar or unipolar)
• Interfaces with Sensor class
• Option to add white noise if the desired ENC is provided, modeled as random delta pulses of charge q_0 with frequency \nu, where ENC^2 = \nu q_0^2 \Integral[f(t)^2 dt], where f(t) is the transfer function with the peak normalized to unity
• Also changed L828, 840 in Sensor::InterpolateTransferFunctionTable for the calculation of t (to not be offset by 0.5*m_tStep), since we evaluate the transfer function for times t = t_sig-t', where t_sig, t' are both already offset