Added (command line) nograph option.
Added (command line) nointeractive option.
Add warning if gradient-based optimizer is used with particle-filtering and offer user choice to change mode-finder
Rewrote the portion of code requesting a user input when non linear filters are used with a gradient based optimization routine.

Closes issues #442 and #443.
Merge branch 'master' into particle_mode_compute
Cosmetic change. Replaced warning(...) by disp(...).
Cosmetic change.
Replaced disp(' ') by skipline().
Cosmetic changes. Use skipline() instead of disp(' ').