Fix a bunch of typos noticed in the comments on the website

Thanks to Pieter Belmans and Emmanuel Kowalski
http://stacks.math.columbia.edu/tag/026N#comment-192
http://stacks.math.columbia.edu/tag/04X5#comment-193
http://stacks.math.columbia.edu/tag/05WA#comment-194
http://stacks.math.columbia.edu/tag/05JA#comment-195
http://stacks.math.columbia.edu/tag/02BF#comment-196
Some updates to desirables.tex