Improvements in the Placet tracking code

The tracking code PLACET simulates beam transport and orbit corrections in linear accelerators. It incorporates single- and multi-bunch effects, static and dynamic imperfections. It has an interface based on both Tcl/Tk and Octave to provide maximum flexibility and easy programming of complex scenarios. Recently, new functionalities have been added to expand its simulation and tuning capabilities, such as: tools to perform beam-based alignment of non-linear optical systems, higher order imperfections in magnets, better tools for integrated feedback loops. Moreover, self-contained frameworks have been created to ease the simulation of CLIC Drive Beam, CLIC Main Beam, and other existing electron machines such as CTF3 and FACET.