Add proof equivelence of having a property for algebraic spaces

Thanks to Kestutis Cesnavicius
http://stacks.math.columbia.edu/tag/03E8#comment-500
faithfull ---> faithful

Thanks to Kestutis Cesnavicius
http://stacks.math.columbia.edu/tag/02W0#comment-503
http://stacks.math.columbia.edu/tag/08LU#comment-504