Allow integers in wmin, wmax, tmin, tmax arguments

[nvaytet]

Fixes #147.

We also fix:

• the case where optimization for a choppers cascade is used in combination with a limits on time or wavelength.
• a bug where the initial frame distance for optimization by choppers was not the same as the source distance (it was always zero)

[jl-wynen]

the case where optimization for a choppers cascade is used in combination with a limits on time or wavelength.

What was broken in this case?

[nvaytet]

the case where optimization for a choppers cascade is used in combination with a limits on time or wavelength.

What was broken in this case?

The time and wavelength limits were simply ignored. See here: we were just taking the min and max of the data.