adding onclick pause option

[ajmendez]

Added the ability to pause the motion of particles by clicking on the canvas. This may be a simple solution to this issue: https://github.com/VincentGarreau/particles.js/issues/88

I did not add it to the onhover mode as that it resets the locations of the particles.

Also, I am not sure which minifier you use so I have not updated the .min.js file.

[P4KM4N]

Thanks @ajmendez that was exactly what I needed!

[matteobruni]

Implemented here https://github.com/matteobruni/tsparticles/commit/de1f69f7faec365d21b8208a830ab47be847b98a