Add new SVG icons for signal creation and update action handlers

- Introduced new SVG icons for various signal types including Zero, Normal distribution, Poisson distribution, Gaussian, Lorentzian, Voigt, Blackbody, Sine, Cosine, Sawtooth, Triangle, Square, Cardinal sine, Linear chirp, Step, Exponential, Logistic, Pulse, Step pulse, Square pulse, Polynomial, and Custom.
- Updated action handlers in `actionhandler.py` to associate the new icons with their respective signal types in both 1D and 2D categories.
- Removed the "Empty" option from the image creation menu documentation.

Author: PierreRaybaut