Algebraic spaces are always over a base scheme

Thanks to Kestutis Cesnavicius
http://stacks.math.columbia.edu/tag/03XX#comment-688
Typos in algebra.tex

Thanks to Keenan Kidwell
http://stacks.math.columbia.edu/tag/00O2#comment-689
http://stacks.math.columbia.edu/tag/065R#comment-690
http://stacks.math.columbia.edu/tag/0519#comment-691
http://stacks.math.columbia.edu/tag/00S0#comment-692
http://stacks.math.columbia.edu/tag/00S1#comment-693
http://stacks.math.columbia.edu/tag/00S2#comment-694
http://stacks.math.columbia.edu/tag/08JZ#comment-701