Additional beam parameters when it is read from file

[myurkin]

Currently ADDA is capable of solving a wide range of scattering problems, which may require modification of definitions of basic scattering quantities like amplitude and Mueller scattering matrices and cross sections. When built-in incident beams are used, ADDA makes its best to automatically account for this definitions and specific parameters of the incidence beam. However, it lacks the required information when the incident field (beam) is read from file. So the idea is to add additional command line options to specify this lacking parameters.

First example was discussed in #300 - the parameter m_in (as described in the manual), or its real part, should be made possible to specify in the command line. For instance, a command line -re_m_in <...>. While trivial to implement, we should take care to safeguard an user from incorrect usage, e.g., in combination with built-in beams. Alternatively, we may look broader and implement an option like -beam_scale <...>, i.e. a general correction to incident beam amplitude or intensity. This will have meaningful usage aslo for built-in beams, e.g., for transformation between system of units.

Another example is the beam vorticity, which will become relevant with the implementation of the Bessel beams (#209). It will slightly affect the transformation of the amplitude matrix under rotation.

/cc @AhmedOthman7 @stefaniagl